Re: [PATCH 2/2] drm/amdgpu: Enable clear page functionality

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On 2023-12-13 9:20, Christian König wrote:
Am 12.12.23 um 00:32 schrieb Felix Kuehling:

On 2023-12-11 04:50, Christian König wrote:
Am 08.12.23 um 20:53 schrieb Alex Deucher:
[SNIP]
You also need a functionality which resets all cleared blocks to
uncleared after suspend/resume.

No idea how to do this, maybe Alex knows of hand.
Since the buffers are cleared on creation, is there actually anything to do?

Well exactly that's the problem, the buffers are no longer always cleared on creation with this patch.

Instead we clear on free, track which areas are cleared and clear only the ones which aren't cleared yet on creation.

The code I added for clearing-on-free a long time ago, does not clear to 0, but to a non-0 poison value. That was meant to make it easier to catch applications incorrectly relying on 0-initialized memory. Is that being changed? I didn't see it in this patch series.

Yeah, Arun stumbled over that as well. Any objections that we fill with zeros instead or is that poison value something necessary for debugging?

I don't think it's strictly necessary. But it may encourage sloppy user mode programming to rely on 0-initialized memory that ends up breaking in corner cases or on older kernels.

That said, I see that this patch series adds clearing of memory in the VRAM manager, but it doesn't remove the clearing for AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE in amdgpu_bo_release_notify and amdgpu_move_blit. This will lead to duplicate work.

I'm also not sure how the clearing added in this patch series will affect free-latency observed in user mode. Will this be synchronous and cause the user mode thread to stall while the memory is being cleared?

Regards,
  Felix



Regards,
Christian.


Regards,
  Felix



So some cases need special handling. E.g. when the engine is not initialized yet or suspend/resume.

In theory after a suspend/resume cycle the VRAM is cleared to zeros, but in practice that's not always true.

Christian.

Alex




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