kindred cape
I am trying to complete an assignment that requires us to do updates on a grid with various thread numbers and compare the speed.
Adding more threads makes no difference, and sometimes even results in worse time.
I do not use java a lot and so am unsure how to analyze my code to see if it is a task granularity problem or something else in the code.
wispy quiverBOT
<@&987246964494204979> please have a look, thanks.
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dire belfry
I am trying to complete an assignment that requires us to do updates on a grid w...
Could you show a code snippet of how you're doing it?
kindred cape
yup, one sec
This is the Main.java that controls the whole thing
public class Main {
public static void main(String[] args) {
long startTime = System.nanoTime();
new GridUpdatev8().run(101, 100000, 3); //array size, iterations, threads
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println("Time taken: " + duration / 1_000_000_000.0 + " seconds");
}
}
And the file is the GridUpdatev8.java class
wispy quiverBOT
This is the Main.java that controls the whole thing
```
public class Main {
...
Detected code, here are some useful tools:
wispy quiverBOT
This is the Main.java that controls the whole thing
```
public class Main {
...
I uploaded your attachments as Gist. This makes them more accessible, for example to mobile users.
deft leaf
Some candidates...
kindred cape
is there a way to tell where my bottleneck is with IntelliJ profiler or a similar tool?
I can't really understand what it's showing me
storm cave
This is the Main.java that controls the whole thing
```
public class Main {
...
make so the outer array is as big as the thread number and inner array is much bigger than 101
wispy quiverBOT
@kindred cape
noble sun
is there a way to tell where my bottleneck is with IntelliJ profiler or a simila...
Are you talking about the profiler's flame graph or just the gutter information after a run?
noble sun
I ran your code through the profiler. Here's what I saw. 75-80% of the time is spent on managing Executor stuff, of that 5% is time waiting on latch.await, so it's mostly task submission that is the slow down. I increased the iteration to 1million to give it more to chew on and runtimes really don't change much. Originally it was 5 to 6 secs, regardless of number of threads used. After bumping iterations to 1million, 53-58sec.
Looking at the timeline feature of the profiler, which shows green/red coloring for time the thread is active/waiting, it shows that almost all the work is begin done in the first thread, and roughly logarithmically less for each additional thread. So number of threads doesn't matter because most of the work is being assigned to the first thread.
I remove the executor completely and just ran single threaded with 1million iterations and it was 22seconds, very different from 53-58seconds. So you can see that even using a single threaded executor is twice as slow (on my machine). So it's no wonder adding more threads just adds more overhead and zero performance gain.
Conclusion: the task you are running, the row calc, is too fine grained.
kindred cape
I ran your code through the profiler. Here's what I saw. 75-80% of the time is ...
thanks for walking me through it, this is exactly what I was looking for
I'll try to find a better way to get things done now that you gave me an idea of how the profiler works.
noble sun
You also need to break up that one huge method into smaller methods otherwise the profiler has nothing to point to other than the one huge method.
If the size of the grid was increased you might see more thread use. Eventually you'll run up against L3 cache boundary though.
Also if you have a newer cpu, you might try Math.fma() for some of that row calc.
https://en.wikipedia.org/wiki/FMA_instruction_set
storm cave
I'll try to find a better way to get things done now that you gave me an idea of...
I told you how
wispy quiverBOT
@kindred cape
stuck grail
Here is how to do it with a newer cpu
