Fix 1D PP tracer test

[wconstab]

Stack from ghstack (oldest at bottom):

• -> Fix 1D PP tracer test #362

forgot to enable tracer for tracer test in the last PR

[kwen2501]

Made a small change:
In tracer mode, we don't require users to provide manual split points, because that is being taken care of by the pipeline_llama_tracer function today:

torchtitan/torchtitan/parallelisms/parallelize_llama.py

Lines 272 to 276 in 54b5fa2

	layers_per_rank = len(model.layers) // parallel_dims.pp
	split_spec = {
	f"layers.{i * layers_per_rank}": SplitPoint.BEGINNING
	for i in range(1, parallel_dims.pp)
	}

[kwen2501]

CI should pass after pytorch/pytorch#127607 is landed.

[wconstab]

Made a small change:
In tracer mode, we don't require users to provide manual split points, because that is being taken care of by the pipeline_llama_tracer function today:

I think this is not the right way to do this. If we want the layer-split to be 'automatic', i think it should be automatic for both frontends, and we can delete the _split_points cmdline arg.

or if we want to have the cmdline arg, we should keep it behaving the same for both frontends.

I'd propose to first keep the arg for both frontends, and then do a PR that makes the cmdline arg optional and uses automation for both PRs.

[kwen2501]

Sounds good to me

[kwen2501]

Re-approve