WASM multithreading starts 4 threads regardless of available CPU cores

[vladmandic]

New way of calculating WASM threads seems to default to 4 regardless of number of actual CPU cores

I have Intel i7 with 6 physical cores (12 logical cores) and AFAIK intention was to use logical cores / 2,
but I end up with 4 WASM threads which is the default.

This was working fine in TFJS 3.3.0 (WASM was starting 6 threads as expected),
then WASM multithreading was broken in 3.4.0
and now it's working, but with reduced number of threads.

Environment: TFJS 3.5.0 with Edge/Chromium 90 on Windows 10 with WASM backend (SIMD and MultiThreading enabled)

[vladmandic]

cc @mattsoulanille as this is likely related to #4957

[mattsoulanille]

Definitely related to #4957, but this is intentional. The wasm backend's threadpool uses logical_cores / 2 threads, but is capped to 4 threads total (so I used the same logic in the PTHREAD_POOL_SIZE flag). It's surprising to me that it was creating more than four in earlier versions.

Perhaps it shouldn't be capped at all. What do you think @lina128?

Ideally, you'd be able to control the number of threads created via a flag. This is not supported yet, but there was some discussion in #4957 about adding support.

[google-ml-butler]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you.

[google-ml-butler]

Closing as stale. Please @mention us if this needs more attention.

[google-ml-butler]

Are you satisfied with the resolution of your issue?
Yes
No