Set devices to 1 when it's just Trainer(accelerator='auto')

[kaushikb11]

What does this PR do?

Set devices to 1 when it's just Trainer(accelerator='auto')

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[justusschock]

Shouldn't we use all available devices for that type of device then?

[kaushikb11]

@justusschock @tchaton

Then what would be the difference between Trainer(accelerator="auto") and Trainer(accelerator="auto", devices="auto") as we would support it soon.

[kaushikb11]

I am putting this PR on hold. IMO, if a user just does Trainer(accelerator="auto"), we should crash it and ask them to pass devices=x or gpus if it had GPUs.(like we do right now)

Rather than assigning only one device for them.
For this particular reason, we support devices="auto". Your thoughts?

@PyTorchLightning/core-contributors

[carmocca]

It could also default to devices="auto" if only accelerator="auto" was passed.

[ananthsub]

@kaushikb11 where is the discussion/issue/RFC describing what these PRs are trying to accomplish? it is very hard to review this without that background.

[akihironitta]

I'm not aware of the context outside this PR at all, but I don't think we should accept this change. If it were more common to use only one device out of multiple devices than using all of them, it'd be fine, but it's not common, right?

In my opinion, it should default to devices="auto" as carmocca suggests because I think that's what users (at least I) expect, or raise an exception asking users to specify devices as kaushikb11 suggests.

[codecov]

Codecov Report

Merging #10192 (ac50b55) into master (305a42c) will decrease coverage by 4%.
The diff coverage is 50%.

@@           Coverage Diff            @@
##           master   #10192    +/-   ##
========================================
- Coverage      92%      89%    -4%     
========================================
  Files         181      181            
  Lines       16424    16424            
========================================
- Hits        15178    14545   -633     
- Misses       1246     1879   +633     

[tchaton]

IMO, I believe accelerator="auto" should be the default and devices become a required argument.

[kaushikb11]

devices is set to auto when it's not passed. Closing the PR.