On Wed, Aug 13, 2014 at 10:50:25AM +0900, Michel Dänzer wrote: > On 12.08.2014 00:17, Jerome Glisse wrote: > > On Mon, Aug 11, 2014 at 12:11:21PM +0200, Thomas Hellstrom wrote: > >> On 08/10/2014 08:02 PM, Mario Kleiner wrote: > >>> On 08/10/2014 01:03 PM, Thomas Hellstrom wrote: > >>>> On 08/10/2014 05:11 AM, Mario Kleiner wrote: > >>>>> > >>>>> The other problem is that probably TTM does not reuse pages from the > >>>>> DMA pool. If i trace the __ttm_dma_alloc_page > >>>>> <https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/ident?i%3D__ttm_dma_alloc_page&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=7898522bba274e4dcc332735fbcf0c96e48918f60c2ee8e9a3e9c73ab3487bd0> > >>>>> and > >>>>> __ttm_dma_free_page > >>>>> <https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/ident?i%3D__ttm_dma_alloc_page&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=7898522bba274e4dcc332735fbcf0c96e48918f60c2ee8e9a3e9c73ab3487bd0> > >>>>> calls for > >>>>> those single page allocs/frees, then over a 20 second interval of > >>>>> tracing and switching tabs in firefox, scrolling things around etc. i > >>>>> find about as many alloc's as i find free's, e.g., 1607 allocs vs. > >>>>> 1648 frees. > >>>> This is because historically the pools have been designed to keep only > >>>> pages with nonstandard caching attributes since changing page caching > >>>> attributes have been very slow but the kernel page allocators have been > >>>> reasonably fast. > >>>> > >>>> /Thomas > >>> > >>> Ok. A bit more ftraceing showed my hang problem case goes through the > >>> "if (is_cached)" paths, so the pool doesn't recycle anything and i see > >>> it bouncing up and down by 4 pages all the time. > >>> > >>> But for the non-cached case, which i don't hit with my problem, could > >>> one of you look at line 954... > >>> > >>> https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/source/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c%23L954&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=e15c51805d429ee6d8960d6b88035e9811a1cdbfbf13168eec2fbb2214b99c60 > >>> > >>> > >>> ... and tell me why that unconditional npages = count; assignment > >>> makes sense? It seems to essentially disable all recycling for the dma > >>> pool whenever the pool isn't filled up to/beyond its maximum with free > >>> pages? When the pool is filled up, lots of stuff is recycled, but when > >>> it is already somewhat below capacity, it gets "punished" by not > >>> getting refilled? I'd just like to understand the logic behind that line. > >>> > >>> thanks, > >>> -mario > >> > >> I'll happily forward that question to Konrad who wrote the code (or it > >> may even stem from the ordinary page pool code which IIRC has Dave > >> Airlie / Jerome Glisse as authors) > > > > This is effectively bogus code, i now wonder how it came to stay alive. > > Attached patch will fix that. > > I haven't tested Mario's scenario specifically, but it survived piglit > and the UE4 Effects Cave Demo (for which 1GB of VRAM isn't enough, so > some BOs ended up in GTT instead with write-combined CPU mappings) on > radeonsi without any noticeable issues. > > Tested-by: Michel Dänzer <michel.daen...@amd.com> >
My patch does not fix the cma bug, cma should not allocate single page into it reserved contiguous memory. But cma is a broken technology in the first place and it should not be enabled on x86 who ever did that is a moron. So i would definitly encourage opening a bug against cma. None the less ttm code was buggy too and this patch will fix that but will only allieviate or delay the symptoms reported by Mario. Cheers, Jérôme > > -- > Earthling Michel Dänzer | http://www.amd.com > Libre software enthusiast | Mesa and X developer -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
