[zbyrne]

Motivation

The plan is to potentially lower the memory footprint of an async workload by reusing a single bounce buffer for all async IOs performed on a stream. To accommodate this the IOs may need to be broken into smaller chunks that fit on the bounce buffer.

Technical Details

• Introduce HIPFILE_ASYNC_BUFFER_SIZE environment variable for controlling the bounce buffer size.
• Add a pinned bounce buffer to hipFile::Stream to be used by async IOs on that stream.
• Modify Fallback::async_io to queue many copies of the host and kernel functions to perform large IOs using the bounce buffer.

Issue Tracking

JIRA ID: AIHIPFILE-235

Test Plan

Running unit tests and system tests on Rowlet.

Test Result

Tests pass.

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/rocm-systems/blob/develop/CONTRIBUTING.md.

[therock-pr-bot]

✅ All Policy Checks Passed

Check	Status	Details
📝 PR Description	✅ Pass	—
⛔ Forbidden Files	✅ Pass	—
🧪 Unit Test	⚠️ Warning	Error: Source/code files changed without an accompanying unit test. Expected: add at least one test file named like test_<name>.py / test_<name>.cpp (or <name>_test.*). Current: code file(s) changed: projects/hipfile/src/amd_detail/async.cpp, projects/hipfile/src/amd_detail/backend/asyncop-fallback.cpp, projects/hipfile/src/amd_detail/backend/asyncop-fallback.h, projects/hipfile/src/amd_detail/backend/fallback.cpp, projects/hipfile/src/amd_detail/backend/fallback.h (+13 more); no test file found
🚫 Draft PR	🔜 To Be Enabled	—
🚩 Feature Flag	🔜 To Be Enabled	—
📊 Code Coverage	🔜 To Be Enabled	—

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[Copilot]

Pull request overview

This PR introduces a per-stream pinned “bounce buffer” for fallback async I/O and updates the fallback async path to split large transfers into multiple chunked CPU-copy + kernel-copy steps, controlled by a new HIPFILE_ASYNC_BUFFER_SIZE environment variable.

Changes:

• Add HIPFILE_ASYNC_BUFFER_SIZE configuration/environment plumbing and expose it via Configuration::asyncBufferSize().
• Allocate and retain a pinned async buffer in hipFile::Stream, and plumb buffer host/dev pointers + size through IStream.
• Update fallback async I/O and memcpy kernel logic to operate on chunked transfers; adjust unit/system tests accordingly.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
projects/hipfile/src/amd_detail/environment.h	Adds constrained unsigned-integral Environment::get overload and async buffer env var declaration.
projects/hipfile/src/amd_detail/environment.cpp	Removes old unsigned-int specialization and adds async_buffer_size() accessor.
projects/hipfile/src/amd_detail/configuration.h	Adds Configuration::asyncBufferSize() API.
projects/hipfile/src/amd_detail/configuration.cpp	Implements async buffer size lookup (default 1 MiB).
projects/hipfile/src/amd_detail/stream.h	Extends IStream with async buffer getters; adds async buffer members to Stream.
projects/hipfile/src/amd_detail/stream.cpp	Allocates pinned per-stream async buffer and exposes getters.
projects/hipfile/src/amd_detail/backend/asyncop-fallback.h	Refactors AsyncOpFallback to use stream-owned bounce buffer and track per-chunk byte counts.
projects/hipfile/src/amd_detail/backend/asyncop-fallback.cpp	Switches async op construction to reuse stream async buffer; removes per-op bounce allocation.
projects/hipfile/src/amd_detail/backend/memcpy-kernel.hip	Updates kernel to copy only a single chunk and coordinate chunk sizing via chunk_bytes_copied.
projects/hipfile/src/amd_detail/backend/fallback.h	Declares new async_io_advance host function.
projects/hipfile/src/amd_detail/backend/fallback.cpp	Chunks fallback async I/O by stream buffer size; adds per-chunk advance host function; updates cpu-copy logic.
projects/hipfile/src/amd_detail/async.cpp	Stops clearing op shared_ptr members in completeOp (resource lifetime change).
projects/hipfile/test/amd_detail/mconfiguration.h	Mocks Configuration::asyncBufferSize().
projects/hipfile/test/amd_detail/mstream.h	Mocks new IStream async buffer methods.
projects/hipfile/test/amd_detail/configuration.cpp	Adds tests for async buffer size env var parsing/defaulting.
projects/hipfile/test/amd_detail/environment.cpp	Adds unsigned-integral overload coverage (contains a test-name typo).
projects/hipfile/test/amd_detail/stream.cpp	Updates stream tests for async buffer allocation and adds failure-path coverage.
projects/hipfile/test/amd_detail/async.cpp	Updates async fallback tests for stream-owned bounce buffer and chunked async behavior.
projects/hipfile/test/system/async.cpp	Updates system tests for chunked kernel semantics and new op fields.

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[gaoikawa]

RE: Introduce HIPFILE_ASYNC_BUFFER_SIZE environment variable for controlling the bounce buffer size.

Since we're adding a new env variable, we should document it on the env variable page. Ex: https://rocm.docs.amd.com/projects/hipFile/en/latest/reference/hipFile-environment-variables.html

[john00003]

The Async path was unfamiliar to me, but I got to learn a ton about it (and how our mocking works) while working through this, thanks for the help with that. LGTM I commented on everything that came to my mind.

[systems-assistant]

TheRock Submodule Bump Activity

Newest first

• 2026-09-01 — Included in TheRock via ROCm/TheRock#7793.