jenson needs his 4th mension tho
#:frog_gone: martty's mesa misadventures
void crow
wanton carbon
he will never let you fondle the bits
void crow
🥹
midnight shore
@dense totem you are hereby obliged to help martty develop this debugger technology
it's already working, just that the rough bits (which is basically everything) need to be addressed
dark vortex
someone do addr2line in aco 🐸
dark vortex
i shall take a look if I can do some fun stuff as well when RMV is landed
raven vortex
it's kinda overdue but I have other priorities right now 🫃
midnight shore
no that's fine there's no deadline
raven vortex
ok
midnight shore
put slight pressure on Daniel as he's blocking the MR 🐸
raven vortex
maybe, as soon as I can get to debugging cases that need debuginfo
I think RT in general would benefit from it
midnight shore
inb4 it completely loses it
oh wait
my current Mr assumes there's one source SPIR-V
when doing byte offsets
I guess that will need to be amended somehow to identify which spv it came from 🐸
perhaps hash (shader identifier) would do?
dark vortex
can you link the mr again? would like to read into it a bit
wanton carbon
it's already working, just that the rough bits (which is basically everything) n...
99% complete, only 99% left
dark vortex
thanks
midnight shore
there's an MR that integrates it into brw (this is incomplete) which would be used as reference
wanton carbon
wanton carbon
vrooooooooooooooooooooooooooooooooooooooooooooooom
gf watched vid and we agreed that i have succeeded in making the most boring video in existence
i hope people read the text 
dark vortex
i didn't really help that much i guess (yet? radvgdb incoming??? 😳😳 😳) but boost is least I can do 
wanton carbon
i was thinking of calling it radbg
dark vortex
sauce reveal 😳 😳 😳
wanton carbon
i cannot in good faith post something that has
resume_wave(true);
fun fact, this actually stops all the waves
dark vortex
lmao
wanton carbon
plus the issue is that i have some code in radv, some in aco, some in umr and some on its own
i want to bring the umr mods over first, then just have a mesa fork
dark vortex
hmm I wonder if we can upstream it someday
wanton carbon
i am sure we can
it would be behind a flag i think
but it needs to be written
aco legwork 🐸
dark vortex
yeah
I was also considering making the actual debugger a separate executable with radv exposing some entrypoints for a backend
not sure how much other people would like a whole new private api tho 🐸
wanton carbon
i don't follow
dark vortex
well I'm thinking of your usual CPU debugger workflow where you launch/attach your app inside of a debugger
wanton carbon
ah this was not clear
this is that
beginning of the video, I "attach"
end of the video, I ctrl-c on the debugger, and the influence ends
well, mostly
dark vortex
ah yeah
I also read your message as "flag" = envvar and that was what I was not sure about, mostly
wanton carbon
well yes
you need some cooperation from aco
but this can be just a flag when you load radv
that aco should generate debuggable shaders
dark vortex
hmm thinking about it again envvar actually sounds fine
wanton carbon
you don't actually need any more cooperation from radv than that, except that you need to import a bo into the target process
but this can be done via a layer
dark vortex
if you want to launch apps from a debugger, execve exists, and otherwise doing something like RADV_SHADER_DEBUGGING=1 ./app seems like a reasonable requirement for attaching
dark vortex
you don't actually need any more cooperation from radv than that, except that yo...
nice
halting the waves behind radv's back 😈
wanton carbon
yep, i implemented that
but its a bit less useful since i wanted the debugger to run on a remote sesh, while the target ran on a local sesh
but if you want to do this kinda "wave edit" stuff i have in the video, you could have them both on the local, ye
maybe useful sometimes
wanton carbon
halting the waves behind radv's back 😈
🤫
dark vortex
ah right 🐸
I kinda forgot that your abilities on the local sesh are, uh, limited while there are halted waves on the gpu
dementia gaming
wanton carbon
currently running the debugger requires root
coz you are really plugging values left and right on the gpu
but if it works nicely, the used stuff can migrate into the kernel
and then it can work without privs
dark vortex
makes sense
autumn notch
not gonna lie, the output is very boring
it would be cool to see the whole screen
with the setting the breakpoint, you stepping it, etc
it's very cool but what you show of it is not, if that makes sense
wanton carbon
with the setting the breakpoint, you stepping it, etc
you overestimate the capabilities lmao
wanton carbon
see i can't have a video of something stepping
by hand
remember that freezes the shit out of the screen
autumn notch
hmm you do it thru code rn?
wanton carbon
so it is stepping automatically
autumn notch
hmm
wanton carbon
it would've been cool to step in there, change v0 to 1.0 and then the pixel turns red
but its not how it works lol
autumn notch
fair do
wanton carbon
i know it be boring
but things freezing up really throws a wrench into making a video
autumn notch
yeah makes sense
it would be neat to see el code, and a bigger explanation
lookin forward to writeup
wanton carbon
yeah toot be bad format for that
so i'll write it up
(guess why this thread really exists 🐸)
wanton carbon
lookin forward to writeup
also i commissioned a banner from gf, hopefully arrives on time to adorn the blagpost
dark vortex
good froge banner
dark vortex
🌬️ https://mastodon.gamedev.place/@martty/109638260677126126
also post this to LGD
wanton carbon
i posted the contents already 🐸
wanton carbon
can almost still write his age with a single hex digit and already demented smh
dark vortex
this is what alcohol Mesa dev does to OUR children’s brains!!!
Like and share 😨
dark vortex
can almost still write his age with a single hex digit and already demented smh
if I’m not mistaken your age and my age would have the same number of bits
wanton carbon
if I’m not mistaken your age and my age would have the same number of bits
ye when both are represented as floats, duh
wanton carbon
wot my 3 character mesa MR was not covered by phoronix, i am shattered
floral viper
Looking forward to the release of MGD (martty giraffix defrogger)
onyx vector
would it not be possible to have a usable system if you run the debuggee on a secondary GPU ?
wanton carbon
possibly, i don't know enough of the inner workings
but if you compile shady to compute, that i think would work on a single gpu too
just launch it on a compute queue
onyx vector
what references did you use to make this happen
is there some comprehensive writeup on how the internals work
or is it mostly gleaned from source and talking to other smellies
floral viper
is there some comprehensive writeup on how the internals work
notfromajedi.gif
onyx vector
i'm only interested in shady stuff anyways
wanton carbon
notfromajaker.dogjiff
i am working on the writeup, which aims to be reasonably comprehensive on the touched bits
onyx vector
are there AMD pdfs explaining how to talk to the command processor, the rings etc ?
wanton carbon
mostly looking at isa docs, radv, amdgpu, amdkfd and rocgdb
floral viper
i am working on the writeup, which aims to be reasonably comprehensive on the to...
is that before or after the depth writeup 
wanton carbon
are there AMD pdfs explaining how to talk to the command processor, the rings et...
no
onyx vector
awesome
wanton carbon
is that before or after the depth writeup <:nervous:836935166437883934>
dw
i have not forgotten
wanton carbon
wanton carbon
awesome
it is only the isa docs, and there are some quite outdated and limited docs on the 3d registers up to SI
wanton carbon
but i kinda went in blind, hoping that it will work, despite not seeing code doing this thing
like gpr writing from the host
but it does work
wanton carbon
would you say the 3d registers pdf is useful
for what purpose?
onyx vector
i'd like to understand how the GPU is talked to in general
midnight shore
why would you want pdf when you can read source (which is less likely to have errata than written docs) and ask people 
wanton carbon
oh not even everyone at amd knows how the CP works
onyx vector
i don't think i'm worth the people's time, i just want to appreciate exactly what martty is doing
wanton carbon
(and I don't just mean Jaker in this case )
midnight shore
amd should get rid of packet format zoo and put a macro expanding thing like NV has
onyx vector
all the experts on AMD HW are employed by Valve so 🐸
wanton carbon
most of what the debugger is doing is through banging at mmio registers
working the CP is a much finer art
onyx vector
but like, the KMD is doing all the talking right
you can't talk to the GPU without coordinating with the KMD and expert that to work
wanton carbon
for the debugger?
onyx vector
in general
wanton carbon
yes, in general, everything goes through the KMD
but for the userspace mmio it is just a relay
the KMD does not understand what is happening
floral viper
Think of it as martty whispering sweet nothings into the cp's ear
I am looking forward to the write-up though
Maybe I'll learn how our own hardware works finally
onyx vector
the secret knowledge, i want it inserted into my brain through a high-speed cable plugged into the back of my neck
wanton carbon
i have chosen the jekyll theme, so i am like 94.3% done
midnight shore
martty.github.io incoming? :frog_demon:
wanton carbon
Maybe I'll learn how our own hardware works finally
implying the writeup isn't just the correct incantation order to evoke the behaviour out of the magic rock
wanton carbon
martty.github.io incoming? :frog_demon:
in fact that link is already live
midnight shore
nice
wanton carbon
snazzy anchors
floral viper
I wonder if gpuopen finally added those after I asked
floral viper
wanton carbon
subscribe for nft tips
dark vortex
newt, frog & toad tips
wanton carbon
meta question, how should i refer to Samuel Pitoiset? like that? handle? Sam P? Pitoiset?
dark vortex
I’d probably use Samuel Pitoiset or hakzsam
assuming this is in context of write up?
wanton carbon
around 3k words already 🐸
wanton carbon
4.5k now, got to the end roughly, ig will be around 5k when i am done
a five parter doorstopper
still have to fill out the code, refs, images, that stuff
dark vortex
bro’s writing a book
wanton carbon
a bruhk
wanton carbon
i hashed out some ideas from what could be done in the future - any more ideas?
Memory violation debugging
No wave filtering required. Once a memory violation is detected, the wave can be stopped and examined from the debugger. Memory violations are generally not precise (the faulting PC is not the one issuing the access), but workarounds could be used to make it so. It might even be possible to stop the context loss from occuring.
Data breakpoints
Just as on the CPU, seems like some registers can be programmed to trap when interesting addresses are accessed.
Fragment debugging
Want to examine a variable written in the FS visually? Just swap out the color VGPRs before they get written!
True compute debugging
Shared memory, nonuniform behaviour is all accessible.
Source level debugging
Needs some significant amount plumbing for sure, but the GLSL -> SPIRV side is done. addr2line support in NIR is being worked on.
Arbitrary code execution
Additional code could be compiled by the debugger, then called by the shader.
Debugging barrier hangs
Waves can be stopped when stuck in barriers, and released to prevent context loss, while diagnosing issues.
Multi-wave debugging
More waves can be trapped and worked on at the same time.
Assertions in shader code
Can trap when hit with a debugger present.
Conditional breakpoints/tracepoints?
wanton carbon
yus
dark vortex
also memory watch points
wanton carbon
thats there
dark vortex
no idea about feasibility
midnight shore
that's already under data breakpoints
dark vortex
oh
midnight shore
also you can construct most of these in software probably anyways
dark vortex
<- cannot read
midnight shore
with some varying degrees of annoyance
floral viper
add time travel debugging
midnight shore
dark vortex
multiverse debugging next pls
midnight shore
also I wouldn't call
Memory violations are generally not precise (the faulting PC is not the one issuing the access), but workarounds could be used to make it so.
workarounds
it should rather be said that the compiler needs to play along for a bit
a software feature
wanton carbon
there is a hw bit that makes mem violations precise
midnight shore
ah I see
wanton carbon
probably it is just forcing accesses to complete until the next instr is chewed
midnight shore
other than that seems good
wanton carbon
the workaround i'd do is saving addr vgprs until accesses complete
so that is a compiler thing
just too many options :S
midnight shore
just say "but needs extra work to make it so"
wanton carbon
don't like "workaround"? 😄
wanton carbon
changed
floral viper
call it a workthrough instead of a workaround
midnight shore
also I'd add a paragraph about this vs renderdoc/pix/etc
midnight shore
ah well renderdoc one should cover things
pix is basically the same in that it instruments shader and then replays things
wanton carbon
i'll share a preview of the articles here before i post them, so i'll ask for some extra 👀 then
autumn notch
Time travel debugging maybe?
floral viper
wanton carbon
did jaker travel back in time to post this idea sooner 
floral viper
yus
autumn notch
Now you're thinking with portal 2 RTX
wanton carbon
remunged:
Memory violation debugging
No wave filtering required. Once a memory violation is detected, the wave can be stopped and examined from the debugger. Memory violations are generally not precise (the faulting PC is not the one issuing the access), but with extra work they can be made so. It might even be possible to stop the context loss from occuring.
Data breakpoints
Just as on the CPU, seems like some registers can be programmed to trap when interesting addresses are accessed.
Fragment debugging
Want to examine a variable written in the FS visually? Just swap out the color VGPRs before they get written!
Conditional breakpoints
Shader or host can evaluate arbitrary (even memory dependent) expressions to trigger breakpoints.
True compute debugging
Shared memory, nonuniform behaviour is all accessible.
Source level debugging
Needs some significant amount plumbing for sure, but the GLSL -> SPIRV side is done. addr2line support in NIR is being worked on.
Arbitrary code execution
Additional code could be compiled by the debugger, then called by the shader.
Debugging barrier hangs
Waves can be stopped when stuck in barriers, and released to prevent context loss, while diagnosing issues.
Multi-wave debugging
More waves can be trapped and worked on at the same time.
Assertions in shader code
Can trap when hit with a debugger present.
Time travel debugging
It is possible to record the entire state evolution of a wave, which afterwards the host can replay, freely stepping forwards and backwards.
get booey'd on, baba
wanton carbon
the bababooey is you
autumn notch
Maybe you could do something like AOP :0
floral viper
rapa nui
autumn notch
the bababooey is you
It's like an onion, this one
floral viper
imagine playing obscure lil indie games that no one has heard about (except us)
wanton carbon
whats AOP? advent ocasio-pointer?
floral viper
advent of pode
autumn notch
But yes, cursed aspect oriented programming where you inject logging in between stuff you care about or do other cross-cutting concerns like dat
floral viper
aspect oriented programming
wanton carbon
But yes, cursed aspect oriented programming where you inject logging in between ...
bit more elaboration plox
floral viper
I looked at two explanations on SO and didn't understand shit 
seems like super OOP from what I can tell
wanton carbon
clep sprinkled some confusion crack on us then left
midnight shore
this is nice
autumn notch
MK ULTRA type beat
midnight shore
But yes, cursed aspect oriented programming where you inject logging in between ...
that sounds like a really weird way to say "tracing"
autumn notch
Well, it's one example of what you can do with it
floral viper
in this moment, I am enlightened (and euphoric)
autumn notch
Aop is more about defining aspects, cross-cutting concerns in your code like logging, error handling, that kind of stuff. Then you patch these aspects in through reflection or somethin
Anyways it'd be really cursed 'cause you'd basically be patching stuff into your spirv
So it's essentially part of the arbitrary code execution bullet point tbf
autumn notch
Anyways
wanton carbon
yeah i am not closer to understanding, but i wouldn't dare to question the fruity one
autumn notch
Tbh I only have a superficial understanding of it too, my dad talked to me about his implementation of it in C# once and a coworker mentioned it for the node-based stuff we were doing, but other than that not much
Essentially you add a prelude or postlude(??) to some unit of work
And it can be good for debugging, logging, synchronising stuff even
Really anything you might want to be handled automagically that would be boilerplate otherwise
floral viper
aspect oriented programming is when the reflection does stuff
autumn notch
Am I speaking chinese or like, what is not understandable about this
autumn notch
I'll have you know hangul is the world's best alphabet
The world's most aspect-oriented alphabet
2023 aspect-oriented incident
wanton carbon
2023 aspect-oriented incident
i wuz her e
but anyways, its not the concept i have trouble with, its more like how it fits here
autumn notch
Well, maybe I misunderstand what you're actually doing tbqh, I shall await your writeup and then comment more
wanton carbon
ok I will write 1 to 0xcafebabe once it is done, please wait kindly
dark vortex
@wanton carbon I hath returned
wanton carbon
now my precision-guided munition-based threats work again 😻
wanton carbon
an unrelated thought - how about a radv ext for loading hsa/isa?
dark vortex
embedded isa was a thought that came up before
midnight shore
an unrelated thought - how about a radv ext for loading hsa/isa?
what do you plan to use that for?
wanton carbon
rocm is a mess
midnight shore
ah
midnight shore
I mean if it were for loading code you enter in debugger's prompt, I'd rather just experiment and try to maybe come up with a more specialized ext
but otherwise it seems like a question targeted at people who would be involved into implementing this rocm-on-radv thing
wanton carbon
embedded isa was a thought that came up before
what was the conclusion?
dark vortex
that there aren't terribly many use cases for this 🐸
wanton carbon
that there aren't terribly many use cases for this 🐸
well, yea
but for testing hw, its the best
eg. figuring out hw bugs 🐸
wanton carbon
https://martty.github.io/posts/radbg_part_1/ aight part 1! please let me know any feedback, no sharing yet pls kthxbai 
floral viper
you mean you don't want me to send this to my coworkers yet?
wanton carbon
this blogpost will explode amd office computers (NOT FAKE)
floral viper
well, let me know when this doesn't blow up our compoopers
wanton carbon
read it on your phone (on the toilet, you pooper)
floral viper
I feel like this sentence could use a comma after the word 'Linux', or the whole "AMD...Linux" clause could be parenthesized, idk
Furthermore, umr, AMD’s user-mode debugging facility for Linux also hinted towards the possibility of manipulating waves for graphics.
I almost forgot that BDA is core now
wanton carbon
not something the OpenGL would teach you
floral viper
this sentence has too many commas (or maybe clauses) methinks. it breaks my parser either way
The most well-known debugger under Linux, GDB, is a flexible software, it has a number of targets, which contain the knowledge on how to translate debugging actions (setting a breakpoint, reading the stackframe…) are implemented on the specific architecture.
I would split it into two sentences and maybe remove the "is a flexible software"
(I hope this is the kind of feedback you are looking for lmao)
wanton carbon
ye def
also for higher level stuff like "boring" "too detailed" and "stop smoking meth"
and especially "i have no idea what you are talking about"
floral viper
this sentence isn't really a question, but I suppose you could keep the question mark as a stylistic choice
But perhaps we can be inspired by what it does to the GPU?
so far I have no suggestions on the content itself. It seems legit
wanton carbon
there isn't much content btqh
but i thought some background is useful
difficult to say how much is enough to make the content enjoyable if you are not versed in the dark arts tho
floral viper
too often do blogs go off into the deep end without proper background, so this is refreshing
people who know the 🦐le stuff already can skip it if they want, but it will be vital for the others
the return buttons on the footnotes are nice
wanton carbon
can take no credit for that, but i agree
floral viper
btw how do you determine if something belongs as a footnote vs in parens vs as a hyperlink?
wanton carbon
i am also debating including "the worlds most boring video" as a (de)motivation at the end of the introduction
floral viper
i am also debating including "the worlds most boring video" as a (de)motivation ...
if you do, you better explain what's going on because that was conchfusing as heck the last time you showed us 😄
wanton carbon
perhaps then it would be wise to include at the end
when everything has already been explained i guess
otherwise i can't say its a veegooper before explaining later what that is
floral viper
my vees feel gooped rn
wanton carbon
same
floral viper
having fully read the thing, I can't wait to see what happens in part 2
I have already blocked all memory I have of being in #1053054445518323732
wanton carbon
spoiler alert: not much
its just about configuring the deq
i may include the very best memes from this thread to keep people from gagging at too much bash
but then in part 3
how does it feel length-wise?
floral viper
kinda short, but then again I already know all this stuff
someone who doesn't will have to unpack it more slowly
wanton carbon
hmm, not sure how much the read time counter at the top lies
floral viper
that felt accurate for me
but technical stuff will always depend on the reader's knowledge level
you should send this to someone outside this post and get their opinion
wanton carbon
get me mum to read about wave status registers
dark vortex
finally something to read while amdvlk is trying to run control
(it is taking literal minutes to start up jaker pls fix)
floral viper
I mean someone who perhaps knows about renderdoc and such, but not necessarily how AMD hardware works
which is closer to the average graphics dev methinks
dark vortex
(it is taking literal minutes to start up jaker pls fix)
i will move the rest of shitting on amdvlk to #1026957683921797120
floral viper
speaking of which, brb
dark vortex
looks good from a quick read, nice work
you forgor to share it in LGD
now I did already
floral viper
it means spread it to the whole world immediately, obviously
dark vortex
i cannot read
wanton carbon
floral viper
what is lgd btw
wanton carbon
what is lgd btw
ligma linux gaming dev discord
floral viper
Pixel has shown me the secret passage
dark vortex
luckily zero people have reacted to it so it effectively did not happen
wanton carbon
its not a huge deal, but ye, wanna polish it up first
dark vortex
while we're at reviewing the draft, ishi's mastodon page link is a link to his maud.social page but on mastodon.gamedev.place
maybe it'd be better to link to maud.social directly
wanton carbon
ye idk how
wanton carbon
i tried 😿
dark vortex
wanton carbon
ahh
wanton carbon
🦐 i
dark vortex
you have a footnote explaining that KMD = kernel mode driver, but you only use KMD once in the entire blog🅱️ost, methinks you could just write "kernel mode driver" here and maybe introduce the abbreviation in a later article if it gets used there more
maybe it'd instead be worth instead adding a footnote to "vector GPR" that they are unrelated to GLSL/HLSL vectors and are just one 32bit value?
floral viper
that's what made me bring up the whole footnote thing hehe
wanton carbon
gonna do sleep then get back to u all
autumn notch
O neat
"Aspiring graphics programmers are sometimes left to scrounge old GDC presentations on performance tips and very little is known about the inner workings of some GPUs - too small to have a devrel contact to give insight."
The "too small to have a devrel contact to give insight" should be the first thing in that sentence imo, since you shift to talking about people in general
fallen nest
"Aspiring graphics programmers too small to have a devrel contact..." is a crisp way to start
autumn notch
"wealth of insight into the inner workings." You could change it to "said inner workings" or something similar, since you're repeating inner workings
autumn notch
"Aspiring graphics programmers too small to have a devrel contact..." is a crisp...
Or "Too small to have a devrel contact, aspiring graphics programmers [...]"
"(unfortunately 3D registers documents are no longer published for new architectures)" feels a bit disconnected from the preceding sentence, you could add a "though" at the start to link between the two
Also is it 3d registers or 3d register
Genuinely unsure
floral viper
Or "Without a devrel contact, small (in stature) graphics developers..."
Imagine being a homunculus graphics dev. So tiny that even your whole body weight can't press a key on a keyboard. Would be a sad life
autumn notch
I'm not quite there yet but if my buddies keep zapping me with that shrink ray I'll have to file for bankrupcy
fallen nest
but you'd be able to climb inside people to cure their brain worms
floral viper
by giving them a lobotomy
autumn notch
"[...] I got curious - I have previously seen [...]" I'd put an "as I had previously seen" there instead
"but the conclusion was" probably "but his conclusion"
fallen nest
I'll be honest, everywhere a hyphen appears needs some refactoring
autumn notch
"(how to recover [...])" to "(how would one recover [...])"
fallen nest
RenderDoc also offers shader debugging - this is achieved by a form of CPU/GPU hybrid emulation of the shader code - since shader behaviour has a lot of implementation dependence, for faithful replay Renderdoc compiles small snippets of shader code, that are ran when the program is stepped, while the shader state is maintained in memory.
RenderDoc also offers shader debugging, which is achieved with a form of hybrid CPU/GPU shader code emulation. Since shader behaviour [sic] has a lot of implementation dependence, for faithful replay RenderDoc compiles small snippets of shader code that run when the program is stepped while the shader state is maintained in memory.
floral viper
You put [sic] after the British spelling
autumn notch
" and arbitrary computation on them (buffer device address)," could say "arbitary computation thereof" if u wanna be fancy, just a nitpick tho
:nouk: when
floral viper
> RenderDoc also offers shader debugging - this is achieved by a form of CPU/GPU...
Btw RenderDoc needs to be capitalized in two places
fallen nest
yeah I deliberately didn't wanna remove his tone, but stuff is just a bit shuffled
fallen nest
too much passive voice
floral viper
Can't tell if that's a jerk or serious
fallen nest
that's like the most annoying english grading comment
I still don't entirely know what passive voice is because I was in the lower level english classes
I assume its just a conspiracy to keep me from hitting word counts
floral viper
It's when American reporters say "the cop's gun was fired" rather than saying "the cop fired the gun"
fallen nest
oh, then yeah that might actually be something to watch out for in this
the sentence indirection gets confusing when you're trying to describe something technical
autumn notch
"although there is an extension VK_EXT_device_fault" could be rephrased as "although the VK_EXT_device_fault extension exists"
"The debugger waits for a signal to happen, then accesses the state of the inferior (reading / writing memory), then resumes it. " that second "then" is superfluous
floral viper
what would you replace it with
autumn notch
nothing
floral viper
it won't make sense then
autumn notch
it's the first one that's superfluous actually
autumn notch
"these trigger when a piece memory is written" I think this is missing an "of"?
not sure, might be a technical term I don't know lmao
autumn notch
this sentence has too many commas (or maybe clauses) methinks. it breaks my pars...
this sentence I'd rewrite as "The most well-known Linux debugger, GDB, is a flexible program with a number of targets which know how to translate debugging actions (setting a breakpoint, reading the stackframe...) to a specific architecture"
fallen nest
it says target ... architecture
so I think it means architecture targets, the way compilers have?
maybe
as in there are builds of gdb for different architectures
not sure how relevant that is to anything
floral viper
oh. I tried interpreting it that way but it confused me
autumn notch
I think it's literally just that gdb has a concept called targets
it does explain it tho
it's a mapping from the gdb concepts to the architecture's way of implementing them I guess
floral viper
I think martty should elaborate on that if he brings it up
autumn notch
I know strictly nothing about gdb ofc
floral viper
Same
autumn notch
ok imma go to bed I'll continue reading after approximately 8 hours of sleep innit
floral viper
Certified bruv moment
autumn notch
Bit cheeky
wanton carbon
i left in some mistakes for u guys to pick at, as a treat :3
floral viper
good morning sweetie
wanton carbon
i'm glad the homunculus angle was not lost, i am striving to be inclusive
floral viper
ong
wanton carbon
nah all good stuff
ye the gdb point was that it essentially lets you add more targets while keeping the ui and all the other shit separate
this is what rocgdb does
wanton carbon
its a piece of code that translates the abstract gdb commands to the specific hw / sw
floral viper
ah, reading the docs explains it
crazy how it be like that
wanton carbon
but dw, this was the primary thing i wanted to learn coz knowledge poisons the mind
its crazy that there be people out there not understanding what a target is, no?
floral viper
my first thought as to what you meant by "target" in the post was indeed correct, but the way it was brought up conchfused me
floral viper
its a piece of code that translates the abstract gdb commands to the specific hw...
rocgdb is AMD’s ROCm based gdb + custom target that can debug compute programs,
I think of target as "target platform", not this exact definition
I guess the way you wrote it in the blog was more in line with the GDB meaning of "target", but to someone who doesn't use GDB, it's confusing
wanton carbon
i will put some more words around that bit to make it clearer
floral viper
those are my 3¢ anyways (due to inflation)
wanton carbon
those are my 3¢ anyways (due to inflation)
so you did end up using harvey
wanton carbon
It's when American reporters say "the cop's gun was fired" rather than saying "t...
but its never phrased as "the cop was fired"
autumn notch
howdy again
wanton carbon
howdy
i am about to upload a renewed version where the hyphens have been murderised
autumn notch
nice
well, there is one hyphen that does make sense so far
I will not say which to keep you on your toes
wanton carbon
i inherited the hyphens from my gramgram, how dare you
autumn notch
😔
"with amdkfd, which is a separate KMD from amdgpu, that graphics applications use."
could be rewritten as "with amdkfd, a separate KMD from amdgpu which graphics applications use"
privileges instead of "privilages"
wanton carbon
ok updated now
autumn notch
noice
I have now finished reading
good stuff
I like that you take it kinda slow
was understandable even for me, a complete neophyte
wanton carbon
thats good news
wanton carbon
nono in fact i will add a tag with "difficulty-level:clep"
autumn notch
I'm honored/insulted
wanton carbon
the natural state of man
floral viper
hinsulted (new win32 type dropped)
floral viper
sometimes when I'm really tired, I'll write typos like that constantly
wanton carbon
tbh i find i make most typos because i start thinking of the next word that should be typed and then i start mixing in the letters
floral viper
sometimes I consider using a spell checker for my blog, but then I don't
then I continue writing raw html (sigma masochistic personality)
wanton carbon
the real spell checkers are the friends we made along the way
onyx vector
The disadvantage of such emulation is that due to computational requirements, emulating larger bodies of work is not currently done, essentially providing a single threaded view of the execution (no cross-invocation or cross-subgroup communication).
I didn't know that... Well renderdoc would have never been useful for me then anyways
wanton carbon
> The disadvantage of such emulation is that due to computational requirements, ...
i think for pixel shader it might run the quad for derivatives
onyx vector
amdkfd and amdgpu can coexist simultaneously?
i thought the former was some kind of headless thing
wanton carbon
wdym? that you run two programs that use either?
onyx vector
both can't be the lowest level device driver, one would have to talk to the other
seems like amdkfd does in fact talk to amdgpu
and used to talk to radeon too
wanton carbon
some of kfd has been merged into amdgpu, but far from all
wanton carbon
seems like amdkfd does in fact talk to amdgpu
dark vortex
posting date is one year behind :)
wanton carbon
onyx vector
indeed: https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/amd/amdgpu...
this begs the question, if radv can run compute shaders on the dedicated compute queue, what does amdkfd even do, just debugger support ?
onyx vector
the post is from Jan 15 though
dark vortex
guess martty intends to release it officially™️ on jan 15?
onyx vector
it's not yet Jan 15 2023 either
wanton carbon
eh it requires me to put a date
wanton carbon
this begs the question, if `radv` can run compute shaders on the dedicated compu...
wdym? it does nothing because radv doesn't talk to amdkfd
onyx vector
how long have you been working on this again
onyx vector
wdym? it does nothing because radv doesn't talk to amdkfd
what does it do for rocm compute that amdgpu doesn't already do for vulkan/gl compoot
onyx vector
so uh
wanton carbon
the other 15 secret queues that exist in the hw
onyx vector
how hard could it be to teach rocgdb to tend to VK cs invocations ? surely not that hard at all then
wanton carbon
zero hard
floral viper
on a scale of zero to zero though
onyx vector
NaN hard
wanton carbon
oh wait rocgdb
onyx vector
yes
wanton carbon
i mean, nothing currently in there does it, so its just putting my code into rocgdb
but why would you wanna strap to the beautiful ecosystem of rocm when you don't have to
why not just put my code into gdb
there isn't really a gain from using rocgdb
onyx vector
the question is, what prevents rocgdb from working with vulkan right now, out of the box
for compoot i mean
wanton carbon
it talks to amdkfd which doesn't know anything about your workload i imagine, because that doesn't go through amdkfd
but tbh i couldn't compile rocm so uhhh
who knows 😄
onyx vector
i just get the packages from ayymd
i got the old rocm support in anydsl dusted off this week to let a student work on a topic with it
(they're gonna try to talk to the RT hw from within rocm basically)
dark vortex
and another one in RDNA3
wanton carbon
what i mean is that they don't FF bits for RT
dark vortex
it's a 100% improvement, try getting that from a NV card
wanton carbon
so there can be no issue doing RT, because it is just software
onyx vector
do we know what nvidia does in detail ?
dark vortex
well everything except the (arguably small) bit the hw does I guess
wanton carbon
whereas on a theoretical CUDA bog, it might require a hand cranked register
also the way rocgdb does debugging is not the way i have implemented, afaik
my way is the legacy way
i think
oh right, now i remember
i think rocgdb does the cwsr form of debugging, where it just pulls a wave from the device
onyx vector
that must hurt
wanton carbon
but tbh i don't grok what rocdbgapi does fully
wanton carbon
i just get the packages from ayymd
but lmk if you try and what happens, afaik at least the documentation talks about PM4 queues
midnight shore
https://martty.github.io/posts/radbg_part_1/ aight part 1! please let me know an...
but the conclusion was that graphics waves are most likely too complex to save and restore (how would one recover rasterization and output state?).
we're not save/restoring graphics waves, I'd just say graphics state here (because it's the rasterizer and FS output state and other bits that can't be save/restored, not shaders)
wanton carbon
> but the conclusion was that graphics waves are most likely too complex to save...
graphics waves cannot be saved and restored (due to additional rasterization and framebuffer state that would also need to be saved and restored)
like this?
midnight shore
almost, but I now have more questions
what is the definition of saving or restoring a wave here
does wave still exist when until it's "restored" or does it need to be "restarted" somehow
because if latter I can see that with graphics we can't do that
and I guess in that case this phrasing is fine
oh well I guess this detail doesn't matter anyway so it's all good
floral viper
what if you said it like this to avoid the implication
because rasterization and framebuffer state cannot be saved and restored, graphics waves also cannot be saved and restored
wanton carbon
in cwsr you quit the wave you have saved the state of, then when you need to restore you relaunch them with the appropriate GPR allocation then trap them immediately to reload the state
midnight shore
in cwsr you quit the wave you have saved the state of, then when you need to res...
I see
let's just say that we can't restore graphics waves then, without note in parens
I misunderstood things initially
wanton carbon
what if you said it like this to avoid the implication
> because rasterization a...
what is the implication Jaker? are you gonna hurt waves?
floral viper
btw what is cwsr
wanton carbon
compute wave save/restore
floral viper
what is the implication Jaker? are you gonna hurt waves?
the implication (afaik) is that raster/fbo state cannot be saved and restored
so why not just say that
midnight shore
the implication (afaik) is that raster/fbo state cannot be saved and restored
no
the important bit is that we can't restart graphics waves
not being able to save/restore FF state would be secondary problem here
floral viper
I thought the inability to restore that state was what killed it, but I guess not
wanton carbon
well its a dual thing - PS waves get launched by FF hw
midnight shore
and the FF hw waits for those waves to complete
so it needs to somehow identify them
wanton carbon
atoclkotamotagi, kinda no way to pull that FF state and put it back
(according to our currently limited knowledge of the arcane machinations of the amd gpu internals)
floral viper
maybe an extra sentence would help clarify things in that paragraph then
wanton carbon
sounds like a plan
floral viper
btw where did you get that screenshot of renderdoc
it looks almost unlike the renderdoc I've seen
wanton carbon
imagine that it is bigger
floral viper
will do
wanton carbon
problem solved 😎
floral viper
Wew this thread has almost 2k messages already. When did you create it?
wanton carbon
Wew this thread has almost 2k messages already. When did you create it?
Dec 18 ish?
wanton carbon
scrolled up, 15
wanton carbon
https://martty.github.io/posts/radbg_part_2/ part II draft (attn: @dark vortex DRAFT)
dark vortex
weow
should’ve told me that before I made a bot that crawls this channel for links and shares them on my linkedin
wanton carbon
phew, i was fearing that it was automatically submitting them to be printed on TP as well
good news
dark vortex
I recommend reinstalling all the packages that are already installed.
might be worth mentioning that to use pacman on deck you need to disable readonly mode
wanton carbon
if only i did that
dark vortex
ah it’s in different section
guess normal people who read from top to bottom will not be affected by this
actually
guess normal people who read from top to bottom will not be affected by this
wanton carbon
more rra
dark vortex
i am actually sadly once again hanging my gpu with bvh builds for no reason
maybe I should apply rra to the code then
from a few more quick looks, looks nice 
onyx vector
shouldn't the withered wojak be the deck
floral viper
the witheredjak is martty
midnight shore
https://martty.github.io/posts/radbg_part_2/ part II draft (attn: <@585830269358...
it's Van Gogh not vangogh
wanton carbon
bruh
midnight shore
van bruh
wanton carbon
u mean Van Bruh
floral viper
van goghment
I finally read the post and it was rather pleasant
I didn't take note of grammatical anomalies, though I did notice some
wanton carbon
no diarrhea?
floral viper
that will come in part 3 I hope
floral viper
I don't remember when we (you?) adopted that, but
this thread is inspiring me to start writing that "other" thing
too bad it's 5:30am and I need to schleep rn
wanton carbon
schleep now, then we should start other thing too, yesyes
wanton carbon
cool stuff, huh
but it is still mbcp
don't think it interferes with the debooger
floral viper
shadow regs are used to optimize shadow mapping
midnight shore
but it is still mbcp
yeah I'm just not sure what this is for
wanton carbon
wdym?
midnight shore
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18301
well what does this MR together with mbcp on achieve that wasn't previously done
I thought it might improve debugging experience in some cases (e.g. debugging non-graphics on GFX queue?) but not sure, just random hypothesis
wanton carbon
i think it just enables gfx preemption
the gfx registers were not saved, so switching corrupts the CP state
wanton carbon
"just" - i don't mean to downplay, its a cool thing
midnight shore
so you're saying graphics waves can be somehow suspended with this and you'll still get usable desktop?
wanton carbon
no
its command level preemption
you drain the waves, switch the CP state, run some other tasks, switch CP back, run next cmd
that is my understanding
midnight shore
I see, so it's just fixing some state being lost/corrupted when preempting?
wanton carbon
yes
midnight shore
I see
wanton carbon
again, thats my understanding
wanton carbon
ok time to make this code 20% less shit
wanton carbon
this meme is from the future, you will need to read part 3 to understand
wanton carbon
i managed to pull the debug enable code into the debugger, no longer need to do it before running the app, thats neat
now lets see what code is actually needed, and what is only there bc of superstition
wanton carbon
i managed to pull the debug enable code into the debugger, no longer need to do ...
(this was bc i misunderstood tf that register does and never unstalled the vmid which just hangs)
fallen nest
this meme is from the future, you will need to read part 3 to understand
I read this and my first thought was "is that some gmod map"
wanton carbon
not until you make it
as suspected, it isn't even needed to stall the vmid lol
in fact, practically nothing is required, i guess i had something else fucked up and went on a wild goose chase lol (sad lol)
wanton carbon
@dark vortex somewhat degarbo'd code here: https://gitlab.freedesktop.org/martty/radbg-poc
still no chance of you running it locally but you can 👀
dark vortex
I shall take a look within 3-5 business days
wanton carbon
if bda so good, explain this
wanton carbon
posted part I on the interwebs, thanks all for being my rra
wanton carbon
floral viper
I don't have twitter either
wanton carbon
i beginning to understand how fwog is so advanced
floral viper
I can only afford to be addicted to one social media platform
wanton carbon
and risk missing a gob meltdown? weird
floral viper
dark vortex
https://mastodon.gamedev.place/@martty/109692612087440655
you frogor lgd for real this time
wanton carbon
you frogor lgd for real this time <:froge:865721361225351176>
you can post it if u want, more forganic that way
dark vortex
i was waiting for the permission
wanton carbon
i was waiting for the permission <:frogapprove:891067328215810059>
ah don't, dw
it was just the draft that i wanted to keep under wraps
wanton carbon
@midnight shore or @raven vortex do you have a good description of what a ring is? am i correct that it is a ringbuffer, that contains the PM4 or other type packets?
raven vortex
A ring is a hardware queue that takes PM4, yeah
raven vortex
Hm wait, it doesn’t quite take PM4, it takes whatever launch commands to IBs (indirect buffers) that contains PM4
dark vortex
do you know if the queueing is implemented using ring buffers?
wanton carbon
do you know if the queueing is implemented using ring buffers?
queueing?
dark vortex
s/queueing/the hardware queue ishi was talking about/
wanton carbon
Hm wait, it doesn’t quite take PM4, it takes whatever launch commands to IBs (in...
but it should be more granular i think than entire IBs
raven vortex
there is IB chaining which is basically a jump command you can place at the end of an IB, but not sure what granular is about
wanton carbon
there is IB chaining which is basically a jump command you can place at the end ...
umr checks the ring halting, it seems a bit too coarse for it to wait for an entire IB to me, but maybe thats just how it is
raven vortex
OK, so we might want to differentiate the literal ring (the queue containing IBs) and the conceptual ring (which is a synonym of the hardware command processor)
wanton carbon
OK, so we might want to differentiate the literal ring (the queue containing IBs...
where did you see the only IB bit? I see amdgpu writing all manner of pm4 to the rings
raven vortex
hmm
I've never looked at how it works tbh
the userspace is definitely recording IBs but maybe the direct submission format is PM4 too
wanton carbon
Hmm
"launch" this IB is def a pm4 packet
i guess having IBs kinda makes ring stopping detection a bit iffy
raven vortex
how is ring halt detection performed by umr?
wanton carbon
looks at if the ring pointers are moving
raven vortex
yeah the interaction with IBs might be a bit sussy then
onyx vector
@wanton carbon I did some messing about with ROCm today and i found that it works just fine without amdkfd at all, only rocgdb cares, also I did manage to bring down the system (well, the desktop really, restarting gdm still fixed it) with a broken kernel, and it failed to recover much like with shady compute shaders on the gfx queue
onyx vector
ofc now that I'm home and I try to repro the problem, the AMD repos go down -_-
wanton carbon
<@122845331934281729> I did some messing about with ROCm today and i found that ...
wdym with works fine without amdkfd? which part?
onyx vector
running rocm programs without rocgdb
onyx vector
this is what rocgdb has to say about that
dark vortex
/long_pathname_so_that_rpms_can_package_the_debug_info 🐸
onyx vector
it's very cursed
their packaging is super brittle too
i'm finding out that having any kernels but the supported one prevents amdgpu-dkms from building
fun times
ah, got the stupid kernel module built, after 3 attempts it caught something instead of hanging
i think this amdkcl module is new
the lack of proper debug info is on us though
wanton carbon
nice sleuthing
ye my conclusion was that it may be better to stay out of the mess that is rocm currently
onyx vector
the problem is how amd understands open-source, yes they publish the source, but they package things up themselves and don't mainline stuff properly
ubuntu has repackaged some of the rocm things, and not only is AMD not acknowledging that, their packages conflict
they have different version schemes too, so if you want rocm-cmake from rocm 5.4, the version number for that is some long-ass string like 3.4.15145131.50400 ... and so ubuntu's rocm-cmake gets installed instead, but that's incompatible
endless fun
AMD also don't seem to give easy instructions for building individual components from source
so you either use their automated mystery meat scripts/megapackages, or you're on your own
dark vortex
some would argue that's not really opensource at all, more like source-available
onyx vector
yes
well no it's MIT i think, so it's proper libre or whatever
but the development process is not that open at all
wanton carbon
any part 3 reviewers awake? https://martty.github.io/posts/radbg_part_3/
wanton carbon
bueno
i will toot this together with part 2 so that the lizard part of my brain doesn't get too much of the drug chemical
dark vortex
noice
shit your initial trap handler mr was more than a month ago???
wtf where is my january, it's like last weekend was new years 😭
Sam Pitoiset
I'd still use hakzsam
wanton carbon
shit did a Sam remain
I thought I eradicated them all
fml
name elongenated
don't really like the SRBM footnote, i'll rework
i should explain VMID instead
dark vortex
yeah that's a bit confoosing
wanton carbon
smh the amdgpu doc is wrong saying there can be 16 concurrent processes
its just 15
wanton carbon
yeah that's a bit confoosing
check now?
wanton carbon
sick burn
dark vortex
my 10 day Linux driver stack experience
wait you had like literally zero experience with anything like that before?
also interesting that you know your way around amdgpu virtual memory management
as part of RMV debugging I tried to follow the codepaths from ioctl entrypoint to where PTEs are updated and I got lost real quick
wanton carbon
do I? now thats news to me 😄
dark vortex
well at least somewhat, or your pc is good at grepping kernel source
wouldn't have found the vega interrupt thingies at all lmao
wanton carbon
heh heh
autumn notch
Wait did part 2 come out during my biweekly crack binge
Also it keeps telling me a new version of the content is available as soon as I open the page
why would I read any further when I know this is the best part
"However of gfx9 and above", rewrite to "However from gfx9 and above" maybe?
floral viper
also, I think the hyphen in the first sentence should be a colon
I think you're supposed to use hyphens for important asides or something (like an important version of parens), idk
depending on the assumed knowledge of the reader, it might be useful to explain in slightly greater detail what "banked registers" are
The second sense in which the term banking is used for registers refers to the splitting of a set of registers into groups (banks) each of which can be accessed in parallel. Using four banks increases the maximum number of accesses supported by a factor of four, allowing each bank to support fewer access ports (reducing area and energy use) for a given effective access count.
https://electronics.stackexchange.com/a/102743
I guess my point is that some people might be confused when you just say "The GPU can have many of a certain type of register, organised into banks." without at least a sentence to explain the implication of banks
I dunno if it's a real problem. It all depends on how much you assume the reader knows or how willing they are to look this stuff up
wanton carbon
good point
i'll add a banner
if you don't know what register banks are, turn off your computer and leave. you are not welcome
nah but good points, i'll make some edits
wanton carbon
> The second sense in which the term banking is used for registers refers to the...
although this is not why they are banked in this case
floral viper
kek even more reason to explain it
wanton carbon
Wait did part 2 come out during my biweekly crack binge
clep you have been in a coma for 25 years
you missed so much
carlo's engine can now render a cube
raven vortex
glad that you figured out what GRBM is, when I was playing with SQTT I looked everywhere but still couldn’t get an idea what that means exactly
wanton carbon
i cannot figure out what it stands for however 😄
G is probably gfx, RB is register bank i guess, and m is martty
fallen nest
green, red, blue, metallic
autumn notch
yeah it seems like driver devs have not yet escaped the primal urge to make every code concept a vague acronym
I don't think I've seen this many in other places
wanton carbon
yeah it seems like driver devs have not yet escaped the primal urge to make ever...
its just more efficient to write bbby, instead of you know what
wanton carbon
thanks all, parts 2 and 3 are up now 🥳 (https://mastodon.gamedev.place/@martty/109735033572188329)
dark vortex
hype hype hype
wanton carbon
the final thing holding back gpgpu
autumn notch
dark vortex
you mean stuff like unhandled page faults? iirc I read somewhere they might go into a trap handler as well
wanton carbon
well, yes and no i guess
mem violations indeed go into the trap handler if enabled
but that makes more sense for the debugger
rather that you could have exceptions by triggering the trap handler, which could use the faulting PC to look up an unwind table, etc. etc.
its not like there is a stack to unwind or something currently, but gob is working on it
dark vortex
that'd be a cursed setup
wanton carbon
are you really alive if you haven't violated the rule of 5 on the gpu?
wanton carbon
sure thing
dark vortex
FWIW not sure if you found it already but I found a trap handler as well
https://github.com/RadeonOpenCompute/ROCR-Runtime/blob/master/src/core/runtime/trap_handler/trap_handler.s
wanton carbon
neat
wanton carbon
smh nobody noticed that i forgor an s_rfe_b64 from the isa snippet
autumn notch
sry my integrated Neuralink compiler was busy lowering my dopamine levels so I would satisfy my cravings for a cold and refreshing Coca Cola™️
wanton carbon
to the gulag with ye
floral viper
to the gulag with ye
the co-lag
wanton carbon
https://www.phoronix.com/news/AMDGPU-Compute-ISA-Debug-Kernel single-handedly forced a megacorp to develop months worth of debugger code in mere days 👏
autumn notch
solar ingot
well done
wanton carbon
also yeah these patches show that i am missing some bits for the trap enablement
ironically i had them before, but removed because they didn't seem to do anything, but I guess the current code might hang sometimes
wanton carbon
https://martty.github.io/posts/radbg_part_4/ once more unto the breach my dear comrades?
autumn notch
for the emperor
dark vortex
@ Bas
(i added a space so it doesn't ping people but) I think you could just leave the @ out
or say Bas Nieuwenhuizen probably
wanton carbon
for the emperor
wanton carbon
or say Bas Nieuwenhuizen probably
felt like handles is the right amount of personalness
dark vortex
well the problem is that handles aren't globally coherent the same
wanton carbon
@ Bas glc slc dlc then
dark vortex
in most other places his handle is bnieuwenhuizen
idk
the blooper reel is great I shall include that as well, should I ever write blogs
also
wanton carbon
ah right, @MaybeBas
floral viper
You misspelled step here
https://martty.github.io/posts/radbg_part_4/#single-stepp-and-wave-trace
Maybe you meant to write "single-schlepp"
midnight shore
use a piece of memory to communicate to the host (👋 hey host! i am in the trap handler now) - if we want to breakpoint on an instruction instead of just the wave, we can now enable single stepping
what does this mean btw
wanton carbon
You misspelled step here
https://martty.github.io/posts/radbg_part_4/#single-ste...
the steppenwolf
wanton carbon
> use a piece of memory to communicate to the host (👋 hey host! i am in the tra...
uhh, wdym
midnight shore
actually nevermind, it just stuck out to me as really weird, but I get now that putting s_trap at the beginning of the wave and single stepping to the intended instruction is just this current thing you're implementing, not how full proper breakpoints would work
wanton carbon
its pretty much how full proper breakpoints would work
except you don't need to roundtrip to the host
floral viper
Why does this heading have an octothorpe at the end of it
https://martty.github.io/posts/radbg_part_4/#busier-waiting
midnight shore
its pretty much how full proper breakpoints would work
huh? I thought with proper breakpoints we'd just put s_trap on the instruction where we want to break or something
instead of putting it at the beginning of the wave and stepping until breakpoint
wanton carbon
perhaps, i just don't know how instruction caches work exactly
so i can guarantee the step one works, but not this one
midnight shore
yeah makes sense
wanton carbon
Why does this heading have an octothorpe at the end of it
<https://martty.github...
i uhh
dual anchoring, maximum stability
midnight shore
there's something called S_ICACHE_INV so I think that could be interesting future direction, you'd run that on trap return I think
wanton carbon
but you set the bp from the host
so you need to find the mmio hook that invalidates icaches
midnight shore
well the halted wave is sitting in trap handler, right?
so you could just put that instruction into the trap handler
wanton carbon
now i don't know what you are proposing then
midnight shore
I think what you might have in mind is: when we already have waves running a program and we set a breakpoint, the breakpoint might be ignored by hw because instruction caches won't be invalidated
is that it?
because I thought we were talking about how we'd resume from a breakpoint/after a breakpoint
wanton carbon
i gtg now, lets continue later
floral viper
that meme at the end hits different
floral viper
overall a pretty good post. I can even comprehend most of it (which is cool, given that I haven't even looked at radv)
The only feedback I have is that hyphens feel a little overused
wanton carbon
The only feedback I have is that hyphens feel a little overused
i removed so many hyphens already
will do another pass
floral viper
I can excuse it as being part of your writing style
wanton carbon
Ye im not a garbage writer but a garbage person, please understand
wanton carbon
because I thought we were talking about how we'd resume from a breakpoint/after ...
So you mean after a wave gets filtered, use instructions to get to a specific instr?
I think the tradeoff here is that you can have a million threads that will hit that instr now
So you need to filter again
wanton carbon
which can be done, sure
wanton carbon
The only feedback I have is that hyphens feel a little overused
smh i had only like 3 left
i guess you are an OG hyphen hater
wanton carbon
because I thought we were talking about how we'd resume from a breakpoint/after ...
we can pick this back up, if you want
midnight shore
So you mean after a wave gets filtered, use instructions to get to a specific in...
I don't think that's what I mean
wanton carbon
then i might need a bit more explanation
midnight shore
ye sorry
to ensure we're on the same track, the breakpoint construct you have in mind is that s_trap is placed on the start of the program and once it's hit, you single step to the instruction that we're intending to break on
right?
wanton carbon
yep
well
more like you select the wave when that first s_trap is hit
then selected waves single step
but yes
midnight shore
yes, right
why can't we replace the instruction we intend to break on with s_trap?
then inside trap handler we could do extra conditions (filtering) and also before we return from trap handler we'd run the intended instruction
perhaps not in this exact form of course, but the idea should be clear
wanton carbon
this should be possible as well
midnight shore
ok now let me remember the root of this discussion
wanton carbon
but wait
midnight shore
anyway, I initially just misinterpreted the step in your write up as suggesting that as the current best method to construct breakpoints
wanton carbon
so how it would work is you'd still trap the wave at the beginning, then replace the instruction with another trap, then in that second trap you need to run the intended instruction for all waves that were originally not trapped, then keep those waves trapped until our originally trapped wave executes the trap, then host debugger time, then back to trap handler, undo the changed instruction, release all waves with icache invl
i think its a bit complex
if i'd knew more about icaches it could be made simpler
midnight shore
so how it would work is you'd still trap the wave at the beginning, then replace...
I don't understand, why do we need to trap the wave at the beginning?
wanton carbon
i don't know the mmio hook for icache invl from the host
so any instr manip has to happen in the trap handler
it can't be through CP because then you can't set breakpoints while stopped
midnight shore
so any instr manip has to happen in the trap handler
why? you could just write s_trap using e.g. SDMA or even directly (if shaders are in visible VRAM) and cache invalidation is covered in two ways:
if we set breakpoint before submitting command buffer, we can invalidate instruction caches (if there's manual action required to begin with) when we submit the command before
if we set breakpoint while shader was halted on a breakpoint, we need to invalidate instruction cache when wave resumes (this would happen inside trap handler)
this is conceptual in my mind of course, and relies on assumption that s_icache_inv does what it says
wanton carbon
well, it depends on what cache s_icache_inv dumps, yes, i'd imagine it is for the current WGP
so thats not enough
if it is more, then it can be enough
i guessed right
midnight shore
I assume you have other waves in mind? I kinda felt like it's fine to just let them run impeded (for the current draw/dispatch) but maybe that needs more thought
(I'm assuming that if we overwrite the first int32 of an instruction with s_trap it will either see the old instruction or s_trap)
wanton carbon
imagine you are stopped in a VS, now you possibly can't set a BP for an FS
midnight shore
riiight
hmm
maybe we should just put s_icache_inv at beginning of all waves then
wanton carbon
i imagine that has perf implications 😄
midnight shore
that's not going to be full speed but better than single stepping through each wave
wanton carbon
but its not each wave
midnight shore
well okay
s_icache_inv but gated behind same filtering thingy as the current approach does
wanton carbon
its just the wave you care about
that could be possible
lets just find the mmio hook
midnight shore
yeah I imagine if there's a way to flush TLB from host in the middle of command buffer exec there must also be a way to dump all caches
wanton carbon
possibly
problems is there are many units with icaches 😄
but i think SQC is a reasonable guess
thats the thing that drives waves
midnight shore
aah, and I guess CLIENT_INVALIDATE_ALL_VMID drops all TLBs?
or perhaps that's something stronger
anyway beside the point
wanton carbon
i think you understand why i did the stepping instead 😄
midnight shore
yes
I certainly do, it's much simpler
I just misinterpreted that line in your write up as suggesting that approach as "the current best one" or something
perhaps not the best way to put it
"what you'd do when building a debugger, that's not a stepping stone thing intended to be replaced later"
midnight shore
i'll reword it
no I didn't mean to say that the way you put it in write up is bad
just that my initial confusion is the cause for this discussion
floral viper
Post on Reddit and I'll upboat
They'll be jelly that you have achieved the second-lowest-level of graphics programming
wanton carbon
should've written the debugger in assembly too smh
wanton carbon
Post on Reddit and I'll upboat
but where, /r/idiotsincars?
floral viper
I was thinking r/okbuddyphd actually
wanton carbon
getting good chuckles out of that sub
autumn notch
I have to confess something
I laughed because of the funny ducks
I don't know what the Brillouin Zone is
I looked at the wikipedia article and instantly experienced ego death
floral viper
that's the point of the sub
too bad people post high school-tier stuff there frequently
wanton carbon
I don't know what the Brillouin Zone is
its like the twilight zone, except in many details that make it somewhat different
floral viper
they're the same, but different