Performance of first initialized NativeList

[shut meadow]

Hello,
I'm dealing with the initial performance spike when the scene loads. After using Profiler, I found that the first initialization of NativeList is more performance consuming than the following initializations of NativeLists.

For testing I created the following basic script:

using UnityEngine;
using Unity.Collections;
using UnityEngine.Profiling;

public class testScript : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        Profiler.BeginSample("test list 1");
        NativeList<int> list1 = new NativeList<int>(10, Allocator.Temp);
        Profiler.EndSample();
        list1.Dispose();

        Profiler.BeginSample("test list 2");
        NativeList<int> list2 = new NativeList<int>(10, Allocator.Temp);
        Profiler.EndSample();
        list2.Dispose();
    }
}

Results for list1:

Results for list2:

Why is the initialization of the first NativeList so different in performance and many times larger than the initialization of the following NativeLists?

Am I doing something wrong? Can the first initialization of the NativeList be optimized?

Thank you 🙂

P.S: I just tried this problem in a new empty project and I have the same problem. I'm using version 2022.2.2f1

[umbral wyvern]

Have you tested in a build? Probably just the jitter.

Typically when benchmarking code you 'warm up' by ignoring the first iteration.

Unless you have aot compiled.

[shut meadow]

@umbral wyvern thank you for answer and informations 😉 This profiler data are from editor profiling. (I found it by accident when I was profiling new part of the code)

I am creating mobile game and for some time I have problem with long scene loading after Unity logo disappears. On old devices it is +-20 seconds and on new devices +- 4 seconds. So when I found this performance spike in Start function I wanted to reduce it.

[shut meadow]

Because I am newbie, sorry for probably bad question... I imagine, that initializing of first variable of type is not "first iteration", because on first call it initializes variable (in my case NativeList) and after that is not performed another iteration. Am I wrong? Thank you for the explanation! 😉

[umbral wyvern]

@shut meadow when profiling this monobehavior code from the editor you are paying the cost of the just-in-time compilation when it hits new code for the first time. This is a common cause of people seeing big spikes on "first time" runs. It has nothing to do with native containers.

[shut meadow]

@umbral wyvern Thank you very much for the explanation, I appreciate it. Have a nice day and good luck in development ! 😉

[umbral wyvern]

You're welcome. To confirm that it's not a problem for your build you can profile your build by attaching the profiler to it.

You can use the auto attach profiler option in the build settings to make sure you catch your start code.