[Feature] Split cross-entropy computation in SP (#5959)

* halfway

* fix cross-PP-stage position id length diff bug

* fix typo

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* unified cross entropy func for all shardformer models

* remove redundant lines

* add basic ring attn; debug cross entropy

* fwd bwd logic complete

* fwd bwd logic complete; add experimental triton rescale

* precision tests passed

* precision tests passed

* fix typos and remove misc files

* update softmax_lse shape by new interface

* change tester name

* remove buffer clone; support packed seq layout

* add varlen tests

* fix typo

* all tests passed

* add dkv_group; fix mask

* remove debug statements

* adapt chatglm, command-R, qwen

* debug

* halfway

* fix cross-PP-stage position id length diff bug

* fix typo

* fix typo

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* unified cross entropy func for all shardformer models

* remove redundant lines

* add basic ring attn; debug cross entropy

* fwd bwd logic complete

* fwd bwd logic complete; add experimental triton rescale

* precision tests passed

* precision tests passed

* fix typos and remove misc files

* add sp_mode to benchmark; fix varlen interface

* update softmax_lse shape by new interface

* add varlen tests

* fix typo

* all tests passed

* add dkv_group; fix mask

* remove debug statements

* add comments

* q1 index only once

* remove events to simplify stream sync

* simplify forward/backward logic

* 2d ring forward passed

* 2d ring backward passed

* fixes

* fix ring attn loss

* 2D ring backward + llama passed

* merge

* update logger

* fix typo

* rebase

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix typo

* remove typos

* fixes

* support GPT

---------

Co-authored-by: Edenzzzz <wtan45@wisc.edu>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

colossalai/shardformer/layer/utils.py

@@ -309,6 +309,9 @@ def split_batch_zigzag(
     """
     sp_size = dist.get_world_size(sp_group)
     sp_rank = dist.get_rank(sp_group)
+    if sp_size == 1:
+        return batch
+
     if isinstance(batch, torch.Tensor):
         batch = [batch]
     seq_dim = seq_dim if seq_dim != -1 else batch[0].dim() - 1
@@ -364,6 +367,9 @@ def split_varlen_zigzag(
     """
     sp_size = dist.get_world_size(sp_group)
     sp_rank = dist.get_rank(sp_group)
+    if sp_size == 1:
+        return batch
+
     if is_2d:
         assert max_seqlen > 0, "max_seqlen must be provided for 2D input"