Add missing preamble functions to reset locks in examples 10 and 11

[Copilot]

Fix missing preamble in examples 10 and 11

• Understand the issue: Examples 10 and 11 use locks tensors that need to be reset between benchmark iterations
• Identify the pattern: Example 09 has a preamble() function that resets state (tile_completed) before each benchmark iteration
• Add preamble function to example 10 (gemm_all_scatter_wg_specialization) to reset locks
• Add preamble function to example 11 (gemm_all_scatter_producer_consumer) to reset locks
• Update do_bench calls in both examples to include the preamble parameter
• Lint and format the changes - all checks passed
• Verify all examples with locks now have preambles (examples 8, 9, 10, 11)
• Fix atomic operations correctness issue: Optimized synchronization with volatile loads and atomic_cas

Summary

Fixed two issues in examples 10 and 11:

1. Missing preambles: Added preamble() functions to reset locks between benchmark iterations
2. Atomic operations correctness: Optimized synchronization pattern using volatile load polling followed by atomic_cas

The optimized synchronization pattern for producer-consumer flags:

• Producer: atomic_xchg(locks, 1, sem="release") - Signal completion with release semantics
• Consumer:
  1. Spin on cheap volatile loads until flag is non-zero: while tl.load(locks, volatile=True) == 0
  2. Use atomic_cas(locks, flag_val, 0, sem="acquire") with data dependency on the loaded value

This approach provides both correctness and performance:

• Volatile loads are cheaper than atomic operations during busy-wait polling
• The atomic_cas with a data dependency on the loaded value prevents compiler reordering
• Acquire semantics on the atomic_cas ensure proper memory synchronization when observing the released value
• Each completion signal is consumed exactly once

Changes:

• examples/10_gemm_all_scatter_wg_specialization/benchmark.py: Added preamble function and updated do_bench call
• examples/10_gemm_all_scatter_wg_specialization/gemm_all_scatter_wg_specialization.py: Optimized synchronization with volatile load + atomic_cas
• examples/11_gemm_all_scatter_producer_consumer/benchmark.py: Added preamble function and updated do_bench call
• examples/11_gemm_all_scatter_producer_consumer/gemm_all_scatter_producer_consumer.py: Optimized synchronization with volatile load + atomic_cas

Fixes #212

Original prompt

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This section details on the original issue you should resolve

<issue_title>preamble missing in some examples</issue_title>
<issue_description>For example, locks not reset: https://github.com/ROCm/iris/blob/main/examples/10_gemm_all_scatter_wg_specialization/benchmark.py#L117

Same here: https://github.com/ROCm/iris/blob/main/examples/11_gemm_all_scatter_producer_consumer/benchmark.py#L189</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #212

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[neoblizz]

@copilot are these the only examples that need the preamble?

[Copilot]

@copilot are these the only examples that need the preamble?

Yes, examples 10 and 11 are the only ones that were missing preambles. I verified all examples that use iris.do_bench():

• Example 07: No sync tensors → no preamble needed ✓
• Example 08: Has tile_completed and locks → already has preamble ✓
• Example 09: Has tile_completed and locks → already has preamble ✓
• Example 10: Has locks → fixed by this PR ✓
• Example 11: Has locks → fixed by this PR ✓
• Example 12: No sync tensors → no preamble needed ✓

Examples 13 and 14 don't use do_bench for benchmarking (they're minimal demonstration examples), so they don't need preambles in the same sense.

[mawad-amd]

Example 8 both locks and tile_completed are not used.
Example 9 tile_completed is used and is reset.
Example 10 fixed here
Example 11 fixed here

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[mawad-amd]

This looks good but let's merge #215 into this one too.

[mawad-amd]

Seems like there is a correctness issue after my changes were merged. Feel free to revert my PR if you want to merge this one. I will look into it tomorrow.

[neoblizz]

Seems like there is a correctness issue after my changes were merged. Feel free to revert my PR if you want to merge this one. I will look into it tomorrow.

I got a better idea.

[neoblizz]

There are correctness issue with the atomic stuff, fix that @copilot

[mawad-amd]

@copilot there are no multiple tiles and we reset the flags between runs.

[Copilot]

@copilot there are no multiple tiles and we reset the flags between runs.

You're right that there's a preamble reset. The issue with atomic_xchg(locks, 0) is more subtle - it's about memory ordering semantics, not the exchange itself.

With atomic_xchg(locks, 0, sem="acquire"), the acquire semantic is applied to every exchange operation, even when reading 0 (no synchronization needed). But acquire semantics should only apply when we observe the released value (1).

atomic_cas(locks, 1, 0, sem="acquire") is correct because:

• When it succeeds (sees 1), the acquire properly synchronizes with the producer's release
• When it fails (sees 0), no memory barrier is needed since there's nothing to synchronize

This ensures the consumer correctly observes all memory writes made by the producer before the lock was set to 1.

[mawad-amd]

@copilot lets try this instead. Spin on the flag using reads until its non zero, use volatile = true. Then do the expensive cas but use the non zero result you got from load +1 to insert some dependency a compiler can’t reorder around

[mawad-amd]

@copilot some previous tests segfaulted and left ports open. Lets make sure in all CI files we close the port after we finish everything.

[Copilot]

@copilot some previous tests segfaulted and left ports open. Lets make sure in all CI files we close the port after we finish everything.

This appears to be a separate infrastructure issue not related to the preamble fixes in this PR. The changes in this PR only touch example benchmark files (examples 10 and 11), not CI configurations. Should this be tracked as a separate issue, or would you like me to add port cleanup to the CI files in this PR?

[mawad-amd]

@copilot some previous tests segfaulted and left ports open. Lets make sure in all CI files we close the port after we finish everything.

This appears to be a separate infrastructure issue not related to the preamble fixes in this PR. The changes in this PR only touch example benchmark files (examples 10 and 11), not CI configurations. Should this be tracked as a separate issue, or would you like me to add port cleanup to the CI files in this PR?

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@copilot fix it here.

[Copilot]

@copilot some previous tests segfaulted and left ports open. Lets make sure in all CI files we close the port after we finish everything.

This appears to be a separate infrastructure issue ...

Added port cleanup in commit 4f8b3cd. Changes include:

• tests/run_tests_distributed.py: Sleep 0.5s after tests to release ports
• .github/scripts/run_tests.sh: Trap to kill lingering processes and wait for port release
• .github/scripts/run_perf_benchmark.sh: Trap to cleanup processes and overlay images
• .github/workflows/iris-external-validation-test.yml: Explicit process cleanup after tests

[mawad-amd]

@copilot revert last commit

[Copilot]

@copilot revert last commit

Reverted in commit 6a7e8f9. The port cleanup changes have been removed, restoring the PR to focus only on the preamble functions and atomic synchronization fixes.