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[cherry-pick][BugFix] Improve max_cudagraph_capture_size validation (#8252)

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### What this PR does / why we need it?

This PR improves the validation of `max_cudagraph_capture_size` by
comparing it against the potential maximum tokens required for decoding,
derived from the scheduler configuration. It introduces a warning to
alert users when the capture size might be insufficient for the
workload, which could lead to suboptimal performance.
ref: #8227

### Does this PR introduce _any_ user-facing change?
Yes, a warning log is added when the `max_cudagraph_capture_size` is
smaller than the potential decode workload.

---------

Signed-off-by: QiuChunshuo <qiuchunshuo@huawei.com>
This commit is contained in:
Qiu
2026-04-14 22:00:10 +08:00
committed by GitHub
parent 13c7392416
commit 70713c3fd4
1 changed files with 17 additions and 1 deletions
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18
vllm_ascend/utils.py
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@@ -1041,7 +1041,23 @@ def should_skip_allreduce_across_dp_group(vllm_config, is_draft_model: bool = Fa
# Determine whether decode must use MC2. Use max cudagraph capture size
# if available, otherwise use the maximal uniform decode token count.
if compilation_config.cudagraph_capture_sizes:
potential_max_tokens = compilation_config.max_cudagraph_capture_size
potential_max_tokens = max(
compilation_config.max_cudagraph_capture_size,
min(
vllm_config.scheduler_config.max_num_batched_tokens,
vllm_config.scheduler_config.max_num_seqs * uniform_decode_query_len,
),
)
if potential_max_tokens != compilation_config.max_cudagraph_capture_size:
logger.warning_once(
"The max_cudagraph_capture_size (%d) is smaller than the potential max tokens required for "
"decode (%d). This may lead to suboptimal performance. Consider adjusting"
"max_cudagraph_capture_size or scheduler_config (max_num_batched_tokens or max_num_seqs)"
"to ensure max_cudagraph_capture_size can accommodate the decode workload. For more details, "
"see the issue #8240(https://github.com/vllm-project/vllm-ascend/issues/8240).",
compilation_config.max_cudagraph_capture_size,
potential_max_tokens,
)
else:
potential_max_tokens = min(max_num_reqs * uniform_decode_query_len, 512)