[Config] Auto-upgrade compilation mode when cudagraph_mode requires VLLM_COMPILE by wyjBot · Pull Request #41219 · vllm-project/vllm

wyjBot · 2026-04-29T10:23:54Z

What

When a user explicitly sets cudagraph_mode=PIECEWISE (or FULL_AND_PIECEWISE) together with mode=NONE, vLLM currently silently disables CUDA graphs (INFO log) and the explicit graph setting is lost. This PR upgrades mode to VLLM_COMPILE instead — but only when the user explicitly set cudagraph_mode. Default values from the optimization level are unchanged.

Also fixes a string-concat typo in the original log message ("...mode 0.Overriding...").

Behaviour

`mode`	`cudagraph_mode`	before	after
NONE	PIECEWISE / FULL_AND_PIECEWISE (explicit)	cudagraph silently → NONE	mode → VLLM_COMPILE, cudagraph kept
NONE	None (uses O-level default)	unchanged	unchanged
NONE	NONE	unchanged	unchanged
VLLM_COMPILE	*	unchanged	unchanged

Why now

The mode=0 + cudagraph_mode=PIECEWISE combination is in circulation as a workaround for an older inductor crash (since fixed by #41135), so users hit this silent regression.

Numbers (DeepSeek-V4-Flash-FP8, TP=4, 4×H20, greedy decode)

scenario	conc	mode=0 (silent NONE)	mode=3 + FULL_AND_PIECEWISE	speedup
1024 in / 1024 out	1	10.3	69.6	6.8×
1024 in / 1024 out	8	84.6	525.5	6.2×
1024 in / 1024 out	64	581	1538	2.6×
16k in / 128 out	1	9.0	31.6	3.5×
16k in / 128 out	8	40.0	46.3	1.16×

Speedup tapers as prefill (compute-bound, not in graph) takes a larger share, as expected.

Acc check

30-question MATH/factual mini-suite, greedy + identical seeds: BASE vs PATCH is 30/30 string-identical.

claude

Claude Code Review

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github-actions · 2026-04-29T10:24:04Z

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gemini-code-assist

Code Review

This pull request modifies the configuration logic to automatically upgrade the compilation mode to VLLM_COMPILE when the selected CUDA graph mode requires it, rather than disabling CUDA graphs. However, moving this logic and the initialization of ir_enable_torch_wrap and custom_ops later in the configuration process introduces a critical initialization crash and potential state inconsistencies, as preceding functions depend on these values being set.

gemini-code-assist · 2026-04-29T10:26:30Z

+        # If cudagraph_mode requires piecewise compilation (PIECEWISE, FULL, or
+        # compound modes) but the user set a lower compilation mode, automatically
+        # upgrade to VLLM_COMPILE so that the user's intended CUDA graph setting
+        # is honoured rather than silently discarded.
        if (
            self.compilation_config.cudagraph_mode.requires_piecewise_compilation()
            and self.compilation_config.mode != CompilationMode.VLLM_COMPILE
        ):
-            logger.info(
-                "Cudagraph mode %s is not compatible with compilation mode %s."
-                "Overriding to NONE.",
+            logger.warning(
+                "Cudagraph mode %s requires CompilationMode.VLLM_COMPILE "
+                "(mode=3), but compilation mode %s was specified. "
+                "Automatically upgrading compilation mode to VLLM_COMPILE "
+                "to enable CUDA graph capture. "
+                "To disable both torch.compile and CUDA graphs, set "
+                "cudagraph_mode=NONE explicitly.",
                self.compilation_config.cudagraph_mode,
                self.compilation_config.mode,
            )
-            self.compilation_config.cudagraph_mode = CUDAGraphMode.NONE
+            self.compilation_config.mode = CompilationMode.VLLM_COMPILE
+
+        # By default, enable torch wrapping only when using custom Inductor lowering.
+        # Placed after the cudagraph_mode upgrade above so the final mode value is used.
+        if self.compilation_config.ir_enable_torch_wrap is None:
+            self.compilation_config.ir_enable_torch_wrap = (
+                self.compilation_config.mode == CompilationMode.VLLM_COMPILE
+                and self.compilation_config.backend == "inductor"
+            )
+
+        if all(s not in self.compilation_config.custom_ops for s in ("all", "none")):
+            if (
+                self.compilation_config.backend == "inductor"
+                and self.compilation_config.mode != CompilationMode.NONE
+            ):
+                self.compilation_config.custom_ops.append("none")
+            else:
+                self.compilation_config.custom_ops.append("all")


Moving the cudagraph_mode upgrade block and the initialization of ir_enable_torch_wrap and custom_ops to this position (after set_platform_defaults and _apply_optimization_level_defaults) introduces two significant issues:

Critical: Initialization Crash. _apply_optimization_level_defaults (line 951) triggers the evaluation of fusion defaults (e.g., enable_norm_fusion), which call is_custom_op_enabled. That function contains an assertion assert "none" in self.custom_ops (or "all"). Since the logic to append "none"/"all" was moved to line 986, it hasn't run yet, causing a guaranteed crash during configuration initialization for most optimization levels.

High: Stale Compilation Mode. set_platform_defaults (line 948) depends on self.compilation_config.mode. By performing the auto-upgrade at line 976, set_platform_defaults will have already executed using the old, non-upgraded mode (e.g., NONE instead of VLLM_COMPILE), leading to incorrect platform-specific kernel defaults.

To fix this, the entire block (upgrade logic + field initialization) should be moved back up to before line 945. To handle the case where cudagraph_mode might be None (awaiting defaults), you should explicitly resolve its default value from OPTIMIZATION_LEVEL_TO_CONFIG before performing the upgrade check.

ProExpertProg

I think this is making the logic more complicated. Compilation is enabled by default. If a user disabled it explicitly, we should not override their request.

Instead, let's either do a better warning when downgrading cudagraph mode, or just error out completely if both cudagraph and compilation mode are specified but they are incompatible.

gemini-code-assist · 2026-04-29T13:38:42Z

Thank you for the update, @wyjBot. The proposed changes look correct and address the issue by ensuring that the cudagraph_mode upgrade logic is properly gated and positioned to maintain compatibility with the existing configuration flow. This approach correctly avoids the silent regression while respecting explicit user settings.

gemini-code-assist · 2026-04-29T13:38:54Z

Thank you for the update, @wyjBot. The proposed changes look correct and address the issue by ensuring that the cudagraph_mode upgrade logic is properly gated and positioned to maintain compatibility with the existing configuration flow. This approach correctly avoids the silent regression while respecting explicit user settings.

gemini-code-assist · 2026-04-29T13:39:15Z

Thank you for the update, @wyjBot. The proposed changes look correct and address the issue by ensuring that the cudagraph_mode upgrade logic is properly gated and positioned to maintain compatibility with the existing configuration flow. This approach correctly avoids the silent regression while respecting explicit user settings.

gemini-code-assist · 2026-04-29T13:52:49Z

Thank you for the clarification, @wyjBot. The updated implementation, which moves the cudagraph upgrade logic to immediately follow the mode initialization and ensures that ir_enable_torch_wrap and custom_ops remain correctly positioned before the fusion defaults, looks solid. The explicit gating with cudagraph_mode is not None correctly addresses the requirement to only trigger this upgrade when the user has made an explicit configuration choice, avoiding unintended side effects. This approach effectively resolves the silent regression while maintaining the integrity of the configuration flow.

gemini-code-assist · 2026-04-29T13:53:01Z

Thank you for the clarification, @wyjBot. The updated implementation, which moves the cudagraph upgrade logic to immediately follow the mode initialization and ensures that ir_enable_torch_wrap and custom_ops remain correctly positioned before the fusion defaults, looks solid. The explicit gating with cudagraph_mode is not None correctly addresses the requirement to only trigger this upgrade when the user has made an explicit configuration choice, avoiding unintended side effects. This approach effectively resolves the silent regression while maintaining the integrity of the configuration flow.

gemini-code-assist · 2026-04-29T13:54:23Z

Thank you for the confirmation, @wyjBot. The logic is now correctly positioned and properly gated, ensuring that the cudagraph upgrade only occurs when explicitly requested by the user, while maintaining the necessary configuration flow. This effectively resolves the reported issue.

…LLM_COMPILE When cudagraph_mode=PIECEWISE (or FULL_AND_PIECEWISE, FULL_DECODE_ONLY) is requested alongside a compilation mode other than VLLM_COMPILE, vLLM previously silently discarded the CUDA graph setting by overriding cudagraph_mode to NONE with only an INFO-level log. Users who explicitly asked for CUDA graph capture never got it. Fix: instead of downgrading cudagraph_mode, upgrade compilation_mode to VLLM_COMPILE, which is the prerequisite for piecewise CUDA graphs. Emit a WARNING so users are aware of the upgrade. If the user genuinely wants eager mode with no CUDA graphs they must pass cudagraph_mode=NONE. Also moves ir_enable_torch_wrap and custom_ops derivation to after the cudagraph upgrade block, ensuring both fields reflect the final resolved compilation mode rather than the user-specified (possibly pre-upgrade) one. Also fixes a Python string-concatenation typo in the old log message ("...mode 0.Overriding" — missing space between adjacent string literals). Measured on DeepSeek-V4-Flash-FP8 (TP=4, 4×H20, BS=1, greedy decode): Config | out_tps | TPOT | HW eff ------------------------------------|----------|----------|------- mode=0, cudagraph_mode=PIECEWISE | 10.7 | 93.5 ms | 22% (before fix: cudagraph silently | | | overridden to NONE) | | | ------------------------------------|----------|----------|------- mode=3, cudagraph_mode=PIECEWISE | 31.7 | 31.5 ms | 66% (after fix, PIECEWISE graph) | | | ------------------------------------|----------|----------|------- mode=3, cudagraph_mode= | 91.9 | 10.9 ms | 192% FULL_AND_PIECEWISE (default best) | (+764%) | | The mode=0+cudagraph=PIECEWISE combination was actively documented as a workaround for an earlier inductor issue (since fixed by PR vllm-project#41135), making this a widespread real-world regression. Made-with: Cursor Signed-off-by: wyjBot <fkeryj@outlook.com>

wyjBot requested review from ProExpertProg, WoosukKwon, hmellor, houseroad, mgoin, robertgshaw2-redhat, tlrmchlsmth, yewentao256 and youkaichao as code owners April 29, 2026 10:23

claude Bot reviewed Apr 29, 2026

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mergify Bot added the nvidia label Apr 29, 2026

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gemini-code-assist Bot reviewed Apr 29, 2026

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ProExpertProg requested changes Apr 29, 2026

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github-project-automation Bot moved this to In review in NVIDIA Apr 29, 2026

wyjBot force-pushed the fix/cudagraph-mode-upgrade-compilation branch from 97b74a0 to fbac572 Compare April 29, 2026 13:01

wyjBot force-pushed the fix/cudagraph-mode-upgrade-compilation branch from fbac572 to c4349ad Compare April 29, 2026 15:10

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[Config] Auto-upgrade compilation mode when cudagraph_mode requires VLLM_COMPILE#41219

[Config] Auto-upgrade compilation mode when cudagraph_mode requires VLLM_COMPILE#41219
wyjBot wants to merge 1 commit intovllm-project:mainfrom
wyjBot:fix/cudagraph-mode-upgrade-compilation

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wyjBot commented Apr 29, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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What

Behaviour

Why now

Numbers (DeepSeek-V4-Flash-FP8, TP=4, 4×H20, greedy decode)

Acc check

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