Update worker_init_fn test for pytorch 1.9 nightly

[awaelchli]

What does this PR do?

Fixes #7396

We can ignore a test for pytorch 1.9 since it successfully implements the seeding for numpy in DataLoader workers.
Here is where it got implemented:
pytorch/pytorch@3b977a0

Thanks @ananthsub for pointing me to the commit.

cc @Borda

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[codecov]

Codecov Report

Merging #7441 (9206798) into master (45143fd) will decrease coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #7441   +/-   ##
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- Coverage      92%     92%   -0%     
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  Files         199     199           
  Lines       12987   12987           
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- Hits        11925   11909   -16     
- Misses       1062    1078   +16     

[ananthsub]

Nice that your initial commit was a reference for the PyTorch fix!

[Borda]

Shall we rather have an arg that spec max wersion as < instead of <=

[Borda]

Or set it just as 1.8 as max without minor numbers?

[awaelchli]

< would be more practical I guess but it would not be obvious from the name if < or <=.
Maybe a different approach would be to have torch_gt, torch_ge, torch_lt, torch_le but that would be more argumens ...
not sure

[Borda]

I may say that more practical would be setting level

• max 1.8.1 will keep 1.8.0, 1.8.1 and ignore 1.8.2 and above
• max 1.8 will keep 1.8.0, 1.8.1, 1.8.x and ignore 1.9.x and above
• max 1 will keep 1.8.0, 1.x and ignore 2.x and above

[justusschock]

+1 for the gt, ge, lt and le. Another option would be to have something like `torch_req='<1.9``. But this would involve more parsing logic.

[ananthsub]

@awaelchli should the pl worker init function when used with PT 1.9 also be a no-op? given that pytorch now sets the seed correctly?

[awaelchli]

for numpy yes, we don't need to worry about it in 1.9+.

But another part of the pl_worker_init_fn is that it derives not only a unique seed for each worker but it makes it also unique across all distributed processes (we do that by incorporating the global_rank into the seed sequence). I don't think 1.9 does that.