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@greg-kwasniewski1 greg-kwasniewski1 commented Nov 25, 2025

The bug was caused by incorrect merging of factory and heuristics transforms. The same weight was sharded by both - without a prior check if the transformation was already applied.

Fixes #9379

Summary by CodeRabbit

  • Refactor
    • Optimized internal weight sharding configuration and transform application processes for improved code consistency and maintainability.

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coderabbitai bot commented Nov 25, 2025

📝 Walkthrough

Walkthrough

Refactored the weight sharding transformation mechanism in sharding.py by replacing direct list appends with calls to a new add() method. This change affects multiple sharding detection and application paths including colwise, rowwise, mamba variants, gather operations, and fallback cases while maintaining functional equivalence.

Changes

Cohort / File(s) Summary
Weight sharding transformation refactoring
tensorrt_llm/_torch/auto_deploy/transform/library/sharding.py
Replaced append operations with add() method calls across colwise, rowwise, mamba, local, gather, and default sharding paths. Updated return value usage patterns for tracking applied shards and ensured consistent WeightShardingInfo entry creation via the new additive interface.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

  • Multiple distinct code paths updated with the same refactoring pattern (colwise, rowwise, mamba variants, gather, default cases)
  • Return value usage from add() method requires verification across all call sites to ensure proper counting and tracking
  • Single file scope simplifies review, but consistency across multiple sharding detection branches necessitates careful verification

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❌ Failed checks (2 warnings)
Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. You can run @coderabbitai generate docstrings to improve docstring coverage.
Description check ⚠️ Warning The PR description briefly explains the bug (incorrect merging of factory and heuristics transforms causing duplicate sharding) and references the fixed issue, but omits critical required sections like detailed description, test coverage, and PR checklist completion details. Add a detailed explanation under the Description section explaining what was changed and why, list relevant test cases under Test Coverage, and ensure all PR checklist items are properly addressed with explanations.
✅ Passed checks (3 passed)
Check name Status Explanation
Linked Issues check ✅ Passed The code changes fix the duplicate sharding transform issue by replacing append operations with an add() method that prevents double-sharding, directly addressing the root cause of issue #9379.
Out of Scope Changes check ✅ Passed All changes in sharding.py are focused on fixing the merging of factory and heuristics transforms, staying within scope of issue #9379.
Title check ✅ Passed The title references fixing merging of sharding transforms between factory and heuristics, which aligns with the summary describing replacement of list append calls with an add() method across sharding paths.
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Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (6)
tensorrt_llm/_torch/auto_deploy/transform/library/sharding.py (6)

572-611: Inconsistent counting: counters increment even if add() fails.

The counters num_shards and num_row_col_shards are incremented regardless of whether add() returns True or False. If a node is already sharded (causing add() to return False), these counters will still increment, leading to misleading log messages about the number of transforms applied.

Compare this to the correct pattern in _process_simple_shard (lines 128-139), which uses int(sharding_config.add(...)) to count only successful additions.

Consider applying this diff to fix the counting:

             if re.match(pattern_regex, module_name):
-                num_shards += 1
                 # we have a match. Get the config for this layer
                 config = tp_plan[key]
                 if config == "colwise":
-                    sharding_config.add(
+                    if sharding_config.add(
                         WeightShardingInfo.from_node(
                             lin_node,
                             split_dim=SplitDimension.COLUMN,
                             rank=rank,
                             world_size=world_size,
                             dist_op=None,
                             min_local_shape=min_local_shape,
                         )
-                    )
-                    num_row_col_shards += 1
+                    ):
+                        num_shards += 1
+                        num_row_col_shards += 1
                 elif config == "rowwise":
-                    sharding_config.add(
+                    if sharding_config.add(
                         WeightShardingInfo.from_node(
                             lin_node,
                             split_dim=SplitDimension.ROW,
                             rank=rank,
                             world_size=world_size,
                             dist_op="all_reduce",
                             min_local_shape=min_local_shape,
                         )
-                    )
-                    num_row_col_shards += 1
+                    ):
+                        num_shards += 1
+                        num_row_col_shards += 1
                 elif config == "mamba":
-                    sharding_config.add(
+                    if sharding_config.add(
                         WeightShardingInfo.from_node(
                             lin_node,
                             split_dim=SplitDimension.COLUMN,
                             rank=rank,
                             world_size=world_size,
                             dist_op=None,
                             min_local_shape=min_local_shape,
                             layer_type=LayerType.MAMBA,
                         )
-                    )
-                    num_row_col_shards += 1
+                    ):
+                        num_shards += 1
+                        num_row_col_shards += 1

618-647: Missing counter increment for local colwise case.

The local_colwise branch (lines 621-630) doesn't increment num_row_col_shards, but the local_rowwise branch (lines 632-642) does. This is inconsistent with the non-local colwise and rowwise cases (lines 586, 598) where both increment the counter.

Apply this diff to add the missing increment:

                         if col_row_action == "colwise":
-                            sharding_config.add(
+                            if sharding_config.add(
                                 WeightShardingInfo(
                                     target_node=lin_node.name,
                                     split_dim=SplitDimension.COLUMN,
                                     rank=rank,
                                     world_size=world_size,
                                     dist_op=None,
                                     min_local_shape=min_local_shape,
                                 )
-                            )
+                            ):
+                                num_row_col_shards += 1
                         elif col_row_action == "rowwise":
-                            sharding_config.add(
+                            if sharding_config.add(
                                 WeightShardingInfo(
                                     target_node=lin_node.name,
                                     split_dim=SplitDimension.ROW,
                                     rank=rank,
                                     world_size=world_size,
                                     dist_op="all_reduce",
                                     min_local_shape=min_local_shape,
                                 )
-                            )
-                            num_row_col_shards += 1
+                            ):
+                                num_row_col_shards += 1

649-677: Good: Pattern matching break prevents duplicate processing.

The break statement on line 677 correctly prevents the same node from being processed by multiple patterns in the factory config. This is essential for avoiding conflicting transforms.

However, the counting for the gather case (line 661) still has the same issue as noted earlier—it increments regardless of whether add() succeeds.

Similar fix needed for lines 651-661:

                 elif "gather" in config:
                     # Simple shard (row + all_gather)
-                    sharding_config.add(
+                    if sharding_config.add(
                         WeightShardingInfo.from_node(
                             lin_node,
                             split_dim=SplitDimension.COLUMN,
                             rank=rank,
                             world_size=world_size,
                             dist_op="all_gather",
                             min_local_shape=1,
                         )
-                    )
-                    num_simple_shards += 1
+                    ):
+                        num_shards += 1
+                        num_simple_shards += 1

946-957: Inconsistent counting: increment without checking add() result.

Similar to the factory config path, num_row_col_shards is incremented unconditionally even if add() returns False.

Apply this diff:

         # shard single row node
-        sharding_config.add(
+        if sharding_config.add(
             WeightShardingInfo.from_node(
                 nodes_to_row_shard[0],
                 split_dim=SplitDimension.ROW,
                 rank=rank,
                 world_size=world_size,
                 dist_op="all_reduce",
                 min_local_shape=min_local_shape,
             )
-        )
-
-        num_row_col_shards += 1
+        ):
+            num_row_col_shards += 1

1023-1036: Inconsistent counting pattern.

The counter num_bmm_shards is incremented without checking if add() succeeded.

Apply this diff for consistency:

-        sharding_config.add(
+        if sharding_config.add(
             BMMShardingInfo(
                 target_node=node.name,
                 rank=rank,
                 world_size=world_size,
                 start_idx=start_idx,
                 end_idx=end_idx,
             )
-        )
+        ):
+            num_bmm_shards += 1
+        
         ad_logger.debug(
             f"Sharding BMM for rank {rank}: batch_size={bmm_batch_size}, start_idx={start_idx}, end_idx={end_idx}"
         )
-
-        num_bmm_shards += 1

1067-1074: Inconsistent counting pattern.

The counter num_moe_patterns is incremented without verifying that add() succeeded.

Apply this diff:

-        sharding_config.add(
+        if sharding_config.add(
             EPShardingInfo.from_node(
                 node,
                 rank=rank,
                 world_size=world_size,
             )
-        )
-        num_moe_patterns += 1
+        ):
+            num_moe_patterns += 1
🧹 Nitpick comments (1)
tensorrt_llm/_torch/auto_deploy/transform/library/sharding.py (1)

248-427: Verify that parameter update transforms are applied successfully.

While the primary weight sharding transforms use add() to prevent duplicates (which is correct), the return values of add() for ParameterUpdateInfo transforms (lines 304-319, 333-337, 408-412) are not checked. If these parameter updates fail to apply due to a duplicate, the function still returns 1 indicating success.

Consider logging a warning when critical parameter updates fail to apply, particularly for the split nodes and conv1d parameters that are essential for correct SSM sharding.

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🔇 Additional comments (3)
tensorrt_llm/_torch/auto_deploy/transform/library/sharding.py (3)

117-140: LGTM! Correct use of add() return value.

The function properly uses the return value of add() to count only the transforms that were successfully added, preventing inflated counts when a node is already sharded.


430-501: LGTM with minor note.

The function correctly applies sharding transforms using add(). While the return values aren't checked here, the calling function manages the overall shard counting, so this is acceptable.


1-1080: Overall approach correctly addresses the reported issue.

The replacement of direct list appends with add() method calls prevents duplicate sharding transforms from being applied to the same node. This should resolve the "a and b must have same reduction dim" error reported in issue #9379, which was likely caused by conflicting transforms when both factory config and heuristics tried to shard the same nodes.

The add() method (defined in sharding_utils.py) checks if a node already has a transform and only adds new transforms if the node hasn't been sharded before, returning True on success and False if rejected. This is the correct approach for merging transforms from multiple sources.

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PR_Github #25743 [ run ] triggered by Bot. Commit: b894d40

@greg-kwasniewski1 greg-kwasniewski1 changed the title [AutoDeploy][Bug-9379] Fixed merging sharding transforms between factory and heuristics [TRTLLM-9379][Fix] Fixed merging sharding transforms between factory and heuristics Nov 25, 2025
@greg-kwasniewski1 greg-kwasniewski1 changed the title [TRTLLM-9379][Fix] Fixed merging sharding transforms between factory and heuristics [https://nvbugspro.nvidia.com/bug/5680312][fix] Fixed merging sharding transforms between factory and heuristics Nov 25, 2025
@greg-kwasniewski1 greg-kwasniewski1 changed the title [https://nvbugspro.nvidia.com/bug/5680312][fix] Fixed merging sharding transforms between factory and heuristics [https://nvbugs/5680312][fix] Fixed merging sharding transforms between factory and heuristics Nov 25, 2025
@github-project-automation github-project-automation bot moved this from Backlog to In review in AutoDeploy Board Nov 25, 2025
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MrGeva commented Nov 25, 2025

@greg-kwasniewski1 my PR just got merged (it got stalled due to many CI issues), I think it covers it
https://github.com/NVIDIA/TensorRT-LLM/pull/9145/files

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PR_Github #25743 [ run ] completed with state SUCCESS. Commit: b894d40
/LLM/main/L0_MergeRequest_PR pipeline #19520 completed with status: 'FAILURE'

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/bot run

@greg-kwasniewski1
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Fix already included and merged in PR #9145 by @MrGeva

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[Bug]: Models fail on error "a and b must have same reduction dim"

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