On Mon, Aug 15, 2016 at 3:06 PM, Felix Kuehling <felix.kuehling at amd.com> wrote: > Patch against current amd-staging-4.6 is attached. Reviewed-by: Alex Deucher <alexander.deucher at amd.com> > > Regards, > Felix > > > On 16-08-13 05:25 AM, Christian König wrote: >> Am 13.08.2016 um 01:22 schrieb Felix Kuehling: >>> [CC Kent FYI] >>> >>> On 16-08-11 04:31 PM, Deucher, Alexander wrote: >>>>> -----Original Message----- >>>>> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On Behalf >>>>> Of Felix Kuehling >>>>> Sent: Thursday, August 11, 2016 3:52 PM >>>>> To: Michel Dänzer; Christian König >>>>> Cc: amd-gfx at lists.freedesktop.org >>>>> Subject: Reverted another change to fix buffer move hangs (was Re: >>>>> [PATCH] drm/ttm: partial revert "cleanup ttm_tt_(unbind|destroy)" v2) >>>>> >>>>> We had to revert another change on the KFD branch to fix a buffer move >>>>> problem: 8b6b79f43801f00ddcdc10a4d5719eba4b2e32aa (drm/amdgpu: >>>>> group BOs >>>>> by log2 of the size on the LRU v2 >>>> That makes sense. I think you may want a different LRU scheme for >>>> KFD or at least special handling for KFD buffers. >>> [FK] But I think the patch shouldn't cause hangs, regardless. >>> >>> I eventually found what the problem was. The "group BOs by log2 of the >>> size on the LRU v2" patch exposed a latent bug related to the GART size. >>> On our KFD branch, we calculate the GART size differently, and it can >>> easily go above 4GB. I think on amd-staging-4.6 the GART size can also >>> go above 4GB on cards with lots of VRAM. >>> >>> However, the offset parameter in amdgpu_gart_bind and unbind is only >>> 32-bit. With the patch our test ended up using GART offsets beyond 4GB >>> for the first time. Changing the offset parameter to uint64_t fixes the >>> problem. >> >> Nice catch, please provide a patch to fix this. >> >>> Our test also demonstrates a potential flaw in the log2 grouping patch: >>> When a buffer of a previously unused size is added to the LRU, it gets >>> added to the front of the list, rather than the tail. So an application >>> that allocates a very large buffer after a bunch of smaller buffers, is >>> very likely to have that buffer evicted over and over again before any >>> smaller buffers are considered for eviction. I believe, this can result >>> in thrashing of large buffers. >>> >>> Some other observations: When the last BO of a given size is removed >>> from the LRU list, the LRU tail for that size is left "floating" in the >>> middle of the LRU list. So the next BO of that size that is added, will >>> be added at an arbitrary position in the list. It may even end up in the >>> middle of a block of pages of a different size. So a log2 grouping may >>> end up being split. >> >> Yeah, those are more or less known issues. >> >> Keep in mind that we only added the grouping by log2 of the size to >> have a justification to push the TTM changes upstream for the coming >> KFD fences. >> >> E.g. so that we are able to have this upstream before we try to push >> on the fence code. >> >> I will take a look at fixing those issues when I have time, shouldn't >> be to complicated to set the entries to zero when they aren't used or >> adjust other entries as well when some are added. >> >> Regards, >> Christian. >> >>> >>> Regards, >>> Felix >>> >>> _______________________________________________ >>> amd-gfx mailing list >>> amd-gfx at lists.freedesktop.org >>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx >> >> > > > _______________________________________________ > amd-gfx mailing list > amd-gfx at lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/amd-gfx >
