| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <53EA0497.6060307@gmail.com> Date: Tue, 12 Aug 2014 14:12:07 +0200 From: Mario Kleiner <mario.kleiner.de@...il.com> To: Jerome Glisse <j.glisse@...il.com>, Thomas Hellstrom <thellstrom@...are.com> CC: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Dave Airlie <airlied@...hat.com>, kamal@...onical.com, ben@...adent.org.uk, LKML <linux-kernel@...r.kernel.org>, "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, m.szyprowski@...sung.com Subject: Re: CONFIG_DMA_CMA causes ttm performance problems/hangs. On 08/11/2014 05:17 PM, 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: >>>>> Resent this time without HTML formatting which lkml doesn't like. >>>>> Sorry. >>>>> >>>>> On 08/09/2014 03:58 PM, Thomas Hellstrom wrote: >>>>>> On 08/09/2014 03:33 PM, Konrad Rzeszutek Wilk wrote: >>>>>>> On August 9, 2014 1:39:39 AM EDT, Thomas >>>>>>> Hellstrom<thellstrom@...are.com> wrote: >>>>>>>> Hi. >>>>>>>> >>>>>>> Hey Thomas! >>>>>>> >>>>>>>> IIRC I don't think the TTM DMA pool allocates coherent pages more >>>>>>>> than >>>>>>>> one page at a time, and _if that's true_ it's pretty unnecessary for >>>>>>>> the >>>>>>>> dma subsystem to route those allocations to CMA. Maybe Konrad could >>>>>>>> shed >>>>>>>> some light over this? >>>>>>> It should allocate in batches and keep them in the TTM DMA pool for >>>>>>> some time to be reused. >>>>>>> >>>>>>> The pages that it gets are in 4kb granularity though. >>>>>> Then I feel inclined to say this is a DMA subsystem bug. Single page >>>>>> allocations shouldn't get routed to CMA. >>>>>> >>>>>> /Thomas >>>>> Yes, seems you're both right. I read through the code a bit more and >>>>> indeed the TTM DMA pool allocates only one page during each >>>>> dma_alloc_coherent() call, so it doesn't need CMA memory. The current >>>>> allocators don't check for single page CMA allocations and therefore >>>>> try to get it from the CMA area anyway, instead of skipping to the >>>>> much cheaper fallback. >>>>> >>>>> So the callers of dma_alloc_from_contiguous() could need that little >>>>> optimization of skipping it if only one page is requested. For >>>>> >>>>> dma_generic_alloc_coherent >>>>> <https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/ident?i%3Ddma_generic_alloc_coherent&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=d1852625e2ab2ff07eb34a7f33fc1f55f7f13959912d5a6ce9316d23070ce939> >>>>> >>>>> andintel_alloc_coherent >>>>> <https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/ident?i%3Dintel_alloc_coherent&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=82d587e9b6aeced5cf9a7caefa91bf47fba809f3522b7379d22e45a2d5d35ebd> >>>>> this >>>>> seems easy to do. Looking at the arm arch variants, e.g., >>>>> >>>>> https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/source/arch/arm/mm/dma-mapping.c%23L1194&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=4c178257eab9b5d7ca650dedba76cf27abeb49ddc7aebb9433f52b6c8bb3bbac >>>>> >>>>> >>>>> and >>>>> >>>>> https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/source/arch/arm64/mm/dma-mapping.c%23L44&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=5f62f4cbe8cee1f1dd4cbba656354efe6867bcdc664cf90e9719e2f42a85de08 >>>>> >>>>> >>>>> i'm not sure if it is that easily done, as there aren't any fallbacks >>>>> for such a case and the code looks to me as if that's at least >>>>> somewhat intentional. >>>>> >>>>> As far as TTM goes, one quick one-line fix to prevent it from using >>>>> the CMA at least on SWIOTLB, NOMMU and Intel IOMMU (when using the >>>>> above methods) would be to clear the __GFP_WAIT >>>>> <https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/ident?i%3D__GFP_WAIT&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=d56d076770d3416264be6c9ea2829ac0d6951203696fa3ad04144f13307577bc> >>>>> flag from the >>>>> passed gfp_t flags. That would trigger the well working fallback. >>>>> So, is >>>>> >>>>> __GFP_WAIT >>>>> <https://urldefense.proofpoint.com/v1/url?u=http://lxr.free-electrons.com/ident?i%3D__GFP_WAIT&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=QQSN6uVpEiw6RuWLAfK%2FKWBFV5HspJUfDh4Y2mUz%2FH4%3D%0A&s=d56d076770d3416264be6c9ea2829ac0d6951203696fa3ad04144f13307577bc> >>>>> needed >>>>> for those single page allocations that go through__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>? >>>>> >>>>> >>>>> It would be nice to have such a simple, non-intrusive one-line patch >>>>> that we still could get into 3.17 and then backported to older stable >>>>> kernels to avoid the same desktop hangs there if CMA is enabled. It >>>>> would be also nice for actual users of CMA to not use up lots of CMA >>>>> space for gpu's which don't need it. I think DMA_CMA was introduced >>>>> around 3.12. >>>>> >>>> I don't think that's a good idea. Omitting __GFP_WAIT would cause >>>> unnecessary memory allocation errors on systems under stress. >>>> I think this should be filed as a DMA subsystem kernel bug / regression >>>> and an appropriate solution should be worked out together with the DMA >>>> subsystem maintainers and then backported. >>> Ok, so it is needed. I'll file a bug report. >>> >>>>> 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. Yes, that makes sense to me. Fwiw, Reviewed-by: Mario Kleiner <mario.kleiner.de@...il.com> -mario -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists