Add Pipeline Parallel (and 2D PP+FSDP) support #161

wconstab · 2024-03-23T00:12:55Z

Stack from ghstack (oldest at bottom):

uses pipeline tracer frontend to extract a graph and partition it into
chunks per stage
hardcodes one schedule (1F1B) for now (need to expose option to switch
schedule and test other schedules)
supports 2D parallelism currently, 3D (TP) is work in progress

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ghstack-source-id: 1490240 Pull Request resolved: #161

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torchtrain/parallelisms/parallelize_llama.py

kwen2501 · 2024-03-29T04:54:44Z

train.py

+        logger.info(
+            f"{Color.blue}Extracting pipeline module for stage {pp_mesh.get_local_rank()}{Color.reset}"
+        )
+        model = pmod.get_stage_module(pp_mesh.get_local_rank())


nit: watch out for rank-stage inequality in case of Interleaved 1F1B.

yea, i need to switch to an interleaved schedule and clean this up

torchtrain/parallelisms/parallelize_llama.py

kwen2501

Thanks a lot for the demo! LGTM!

[ghstack-poisoned]

traced module is burning in a 'meta' device arg for one 'ones' op which breaks runtime after moving model to 'cuda'. Haven't worked on loss fn yet. ghstack-source-id: 47735f6 Pull Request resolved: #161

[ghstack-poisoned]

Haven't worked on loss fn yet. ghstack-source-id: 4c438dd Pull Request resolved: #161

[ghstack-poisoned]

(fake) Loss now runs and propagates to logger ghstack-source-id: b5a2908 Pull Request resolved: #161

[ghstack-poisoned]

Loss now runs and propagates to logger, but optimizer isn't working ghstack-source-id: 56b0ef0 Pull Request resolved: #161

[ghstack-poisoned]

Loss now runs and propagates to logger, but optimizer isn't working ghstack-source-id: 4ede08f Pull Request resolved: #161

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now - supports 1D parallelism currently. WIP: support 2D/3D parallel and clean up seed-checkpoint ux ghstack-source-id: 7055ffe Pull Request resolved: #161

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: 6bd8013 Pull Request resolved: #161

kwen2501

LGTM!
Thanks for pulling PP in!

torchtitan/parallelisms/parallelize_llama.py

kwen2501 · 2024-05-02T16:48:27Z

torchtitan/parallelisms/parallelize_llama.py

+        print("labels: ", labels.shape, labels.dtype)
+
+        # Create a pipeline representation from the model
+        pipe = pipeline(model, parallel_dims.pp, example_args=(input_ids,))


nit: strictly speaking, the second arg is the number of microbatches -- it is okay if you using PP dim to represent it for now. Longer term I think it should be exposed as a field in the config file.

torchtitan/parallelisms/parallelize_llama.py

train.py

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requirements.txt

torchtitan/models/llama/model.py

torchtitan/parallelisms/parallelize_llama.py

wanchaol · 2024-05-02T17:02:07Z

torchtitan/parallelisms/parallelize_llama.py

+            )
+
+        # Get example input
+        label_shape = input_shape = (8, 2048)  # TODO


hmmm would PP be working for all cases that are not this shape, or it requires the shape to be the exact input shape of the runtime?

need to double check how this works and fix.

wanchaol · 2024-05-02T17:03:43Z

torchtitan/parallelisms/parallelize_llama.py

+            # TODO(whc) need to fix PP + FSDP-mixed-precision
+            # tracer for PP assumes f32 and is caught off guard when runtime FSDP interacts using bf16 inputs
+            # param_dtype=torch.bfloat16, reduce_dtype=torch.float32
+            param_dtype=torch.float32,


we shouldn't by default change this, this would make the cases where FSDP or FSDP + TP use fp32 instead of bf16

I wonder if supporting bf16 should be a criteria for landing. I would imagine that training with FSDP + PP in fp32 is not really viable efficiency-wise (at least for larger jobs).

I think we should fix this before landing the PP change. I think there was a possible way to fix this in the tracer, but lost track of it, will dig it up

torchtitan/parallelisms/parallelize_llama.py

wanchaol · 2024-05-02T17:07:09Z

train.py

+    # there are virtual stages
+    if parallel_dims.pp_enabled:
+        stage = PipelineStage(
+            pipe=pipe_meta,


should this be pipe_meta or model?

its correct. Ke proposed an alternative, but we'd still have to pass the pipe_info and the model into _PipelineStage in that case. I could make this change.

wanchaol · 2024-05-02T17:09:14Z

train.py

+            pipe=pipe_meta,
+            stage_index=pp_rank,
+            device=device,
+            group=pp_mesh.get_group(),


wondering if we should put the stage creation into parallelize_llama, IMO we only need pp_schedule in train.py

yea, I think this question and Ke's suggestion about returning a PipelineStage from parallelize_llama are better taken in context of a next PR that also adds support for looped schedules.

Looped schedules further complicate things bc the PP logic first needs to chunk up the model, then apply the DP/TP portion of parallelize_llama on each chunk, and finally pass all the chunks into the schedule.

I think in the end, I might prefer to separate out PP from parallelize_llama, and have a flow where we can take the return from PP apply function and iteratively call parallelize_llama on those chunks.

wanchaol · 2024-05-02T17:12:42Z

train.py

+                loss = (
+                    torch.mean(torch.stack(losses))
+                    if is_last_stage
+                    else torch.Tensor([-1.0])


Why we need the default -1 value? because of logging purpose?

oh, yea i could make it a 'None' but then i have to update logger to not log at all. maybe that's actually a better way to do it. let me try that.

ok- so what I could do is try to alter the metrics code so that on non-last-stage ranks, we omit printing loss, or, we print "loss: None" instead of -1.

The change will add more lines of code, since I need to deal with several places that expect loss and global_[avg/mean]_loss to be valid numbers

avoid writing them into metrics dict

replace their format string with a string value instead of a float value in the logger.info

avoid calling loss.item() in the first place

I agree in principle that's the "right" fix, but i'm not sure if its worth the LOC / complexity. I don't totally hate the -1 thing.

Another option I considered is to skip the whole codeblock of '# log metrics' on non-last-stage ranks. I ruled this out, since it is still useful to log mfu, memory for other ranks.

So let me know what you want to do here @wanchaol

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: 205f8b0 Pull Request resolved: #161

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: cbbb628 Pull Request resolved: #161

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: 94f89f9 Pull Request resolved: #161

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: ac8c371 Pull Request resolved: #161

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: feb45e1 Pull Request resolved: #161

wconstab · 2024-05-03T19:00:53Z

torchtitan/parallelisms/parallelize_llama.py

+        for i in range(1, parallel_dims.pp)
+    }
+    # Get example input
+    label_shape = input_shape = (8, 2048)  # TODO


@kwen2501 any ideas for a clean way to do this in torchtrain? do we expect people to get a batch out of their dataloader and then reset it? or do we expect people to hardcode it?

i think what i might do is directly pass input_shape from train.py,

and in train.py i can set input_shape = (job_config.batch_size, job_config.seq_len) or something. is that clean enough?

ok pushed a variation on this.

not sure if its better to hide this inside parallelize since we already have job config, or make it explicit from train.py that we are passing input_shape in for some reason

Either way sounds okay to me -- eventually, the shape comes the config.

[ghstack-poisoned]

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: 0616a1c Pull Request resolved: #161

tianyu-l · 2024-05-07T05:12:10Z

torchtitan/parallelisms/parallelize_llama.py

+    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)


I'm new to PP api and have a question:
If layers_per_rank = 5, parallel_dims.pp = 2, what should be the split_spec. My straightforward thought is SplitPoint.BEGINNING should contain i = 1, 3, 5, but according to the code it's just i = 1.

parallel_dims.pp refers to the number of pipeline stages we split the model into.
For example, if model.layers = 10, 10 // 2 = 5, then we put 5 layers per stage (i.e. layers_per_rank = 5).
Hence we make a cut at model.layers.5 -- (nRanks - 1) split points.

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wconstab · 2024-05-10T21:59:27Z

squashed

- dcp load seems to work now - need to pull in schedule object ghstack-source-id: cbbb8c9 Pull Request resolved: #161

- uses pipeline tracer frontend to extract a graph and partition it into chunks per stage - hardcodes one schedule (1F1B) for now (need to expose option to switch schedule and test other schedules) - supports 2D parallelism currently, 3D (TP) is work in progress ghstack-source-id: 0616a1c Pull Request resolved: #161

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WIP integrate pippy's tracer frontend

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ghstack-source-id: 1490240 Pull Request resolved: #161

facebook-github-bot added the CLA Signed This label is managed by the Meta Open Source bot. label Mar 23, 2024

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Add support for seed checkpoint creation for meta-init flow #172

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wip pipelinestage #174

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Unflatten traced module pytorch/PiPPy#954

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WIP integrate pippy's tracer frontend

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Haven't worked on loss fn yet. ghstack-source-id: 4c438dd Pull Request resolved: #161

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wconstab added a commit that referenced this pull request Apr 3, 2024

WIP integrate pippy's tracer frontend

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(fake) Loss now runs and propagates to logger ghstack-source-id: b5a2908 Pull Request resolved: #161

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wconstab added a commit that referenced this pull request Apr 3, 2024

WIP integrate pippy's tracer frontend

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Loss now runs and propagates to logger, but optimizer isn't working ghstack-source-id: 56b0ef0 Pull Request resolved: #161

wconstab added a commit that referenced this pull request Apr 3, 2024

WIP integrate pippy's tracer frontend

296c875

Loss now runs and propagates to logger, but optimizer isn't working ghstack-source-id: 56b0ef0 Pull Request resolved: #161

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Make freqs_cis a persistent buffer for pp init #201

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Delete grad scaler, which is unsupported/unused #202

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Factor out loss_fn to share code with pipeline par #203

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wconstab added a commit that referenced this pull request Apr 5, 2024

WIP integrate pippy's tracer frontend

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Loss now runs and propagates to logger, but optimizer isn't working ghstack-source-id: 4ede08f Pull Request resolved: #161

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wconstab changed the title ~~WIP integrate pippy's tracer frontend~~ Add Pipeline Parallel support Apr 5, 2024

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Remove unnecessary .to() inside model forward #298

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Add Pipeline Parallel (and 2D PP+FSDP) support #318

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WIP integrate pippy's tracer frontend

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- dcp load seems to work now - need to pull in schedule object ghstack-source-id: cbbb8c9 Pull Request resolved: #161

Add Pipeline Parallel (and 2D PP+FSDP) support #161

Add Pipeline Parallel (and 2D PP+FSDP) support #161

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