tree 509398b515f4b2f0c05b9d093406d2c26c4d5154
parent 62a4c807b0f9baee6de30f2ce1bbc51e98b0455d
author carlobertolli <carlo.bertolli@amd.com> 1705941022 -0600
committer Copybara-Service <copybara-worker@google.com> 1705941362 -0800

[OpenMP] Enable automatic unified shared memory on MI300A. (#77512)

This patch enables applications that did not request OpenMP
unified_shared_memory to run with the same zero-copy behavior, where
mapped memory does not result in extra memory allocations and memory
copies, but CPU-allocated memory is accessed from the device. The name
for this behavior is "automatic zero-copy" and it relies on detecting:
that the runtime is running on a MI300A, that the user did not select
unified_shared_memory in their program, and that XNACK (unified memory
support) is enabled in the current GPU configuration. If all these
conditions are met, then automatic zero-copy is triggered.

This patch also introduces an environment variable OMPX_APU_MAPS that,
if set, triggers automatic zero-copy also on non APU GPUs (e.g., on
discrete GPUs).
This patch is still missing support for global variables, which will be
provided in a subsequent patch.

Co-authored-by: Thorsten Blass <thorsten.blass@amd.com>
GitOrigin-RevId: ae99966a279601022d2b4d61dfbec349f7d65c12