Am 15.08.2016 um 23:03 schrieb Alex Deucher: > 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> Reviewed-by: Christian König <christian.koenig 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 >>
