Compute example counter sampling not working on M4

[LouisChouraki]

Hello,

When running the compute example on a M4 Pro, the duration displayed is always 0ns, no matter the input size (I modified the code to print it as nanoseconds instead of microseconds). But the example works fine on M1-M3. I would assume this generalizes to all M4 chips but I couldn't test it.

I wanted to know if someone has an idea of what could explain this (and ideally how to fix this) as I didn't find much about it online.

[cwfitzgerald]

Hmm, nothing comes to mind, but I haven't personally played around with an M4

[LouisChouraki]

That's unfortunate.. I implemented a profiler to analyze most GPU-time consuming operators in graphs but numbers seems wrong.
Total GPU time adds up to total CPU time but per-operator times are wrong (for example, matmul reports 3% of the GPU usage when I know it is more about 60% if I remove them). But this is behavior is not observed on M1.
My first intuition was that thread concurrency or pipeline cascading kind of mess up the counter sampling, but I cannot find anything about it. It also feels strange I am the first noticing this