Skip to content

minor: zero workspace buffer init for flashinfer trtllm-gen attn #22603

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 3 commits into
base: main
Choose a base branch
from
+4 −4
Open

minor: zero workspace buffer init for flashinfer trtllm-gen attn #22603

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
7327d0a
init
yyihuang Aug 10, 2025
2f56b6a
upd test
yyihuang Aug 10, 2025
963518a
upd
yyihuang Aug 11, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 2 additions & 2 deletions tests/kernels/attention/test_flashinfer_trtllm_attention.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,7 @@ def test_flashinfer_trtllm_decode_with_baseline(
kv_indices = torch.tensor(kv_indices, dtype=torch.int32)
kv_last_page_lens = torch.tensor(kv_last_page_lens, dtype=torch.int32)

workspace_buffer = torch.empty(128 * 1024 * 1024, dtype=torch.int8)
workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.int8)
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

high

The workspace buffer is created with torch.int8 dtype, while the main implementation in vllm/v1/attention/backends/flashinfer.py uses torch.uint8. While this might not cause issues with a zero-initialized buffer, using an inconsistent data type can lead to subtle bugs if the underlying kernel has specific expectations about the data being signed or unsigned. For consistency and to prevent potential correctness issues, it's recommended to use torch.uint8 here.

Suggested change
workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.int8)
workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.uint8)

wrapper = flashinfer.BatchDecodeWithPagedKVCacheWrapper(
workspace_buffer,
kv_layout,
Expand Down Expand Up @@ -247,7 +247,7 @@ def test_flashinfer_trtllm_prefill_with_baseline(
kv_indices = torch.tensor(kv_indices, dtype=torch.int32)
kv_last_page_lens = torch.tensor(kv_last_page_lens, dtype=torch.int32)

workspace_buffer = torch.empty(128 * 1024 * 1024, dtype=torch.int8)
workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.int8)
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

high

The workspace buffer here is created with torch.int8, which is inconsistent with the torch.uint8 used in the main implementation. To ensure consistency across the codebase and avoid potential issues related to signed versus unsigned byte interpretation by the FlashInfer kernel, it is advisable to use torch.uint8 for this buffer as well.

Suggested change
workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.int8)
workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.uint8)

wrapper = flashinfer.BatchPrefillWithPagedKVCacheWrapper(
workspace_buffer, kv_layout)
wrapper.plan(q_indptr,
Expand Down
2 changes: 1 addition & 1 deletion vllm/attention/backends/flashinfer.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -204,7 +204,7 @@ def __init__(self, runner):

def _get_workspace_buffer(self):
if self._workspace_buffer is None:
self._workspace_buffer = torch.empty(
self._workspace_buffer = torch.zeros(
FLASHINFER_WORKSPACE_BUFFER_SIZE,
dtype=torch.uint8,
device=self.runner.device)
Expand Down
2 changes: 1 addition & 1 deletion vllm/v1/attention/backends/flashinfer.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -251,7 +251,7 @@ def __init__(self, kv_cache_spec: AttentionSpec, layer_names: list[str],

def _get_workspace_buffer(self):
if self._workspace_buffer is None:
self._workspace_buffer = torch.empty(
self._workspace_buffer = torch.zeros(
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Also need to update in vllm/attention/backends/flashinfer.py

Copy link
Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Updated. Thanks for your review!

Copy link
Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Sorry for accidentally pushing to another PR. It's added now.

FLASHINFER_WORKSPACE_BUFFER_SIZE,
dtype=torch.uint8,
device=self.device)
Expand Down