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From: "Christian König" <ckoenig.leichtzumerken@gmail.com>
To: Madhav.Chauhan@amd.com, dri-devel@lists.freedesktop.org
Cc: Ray.Huang@amd.com
Subject: drm/ttm: new TT backend allocation pool
Date: Sun, 25 Oct 2020 16:40:47 +0100	[thread overview]
Message-ID: <20201025154100.16400-1-christian.koenig@amd.com> (raw)

This replaces the spaghetti code in the two existing page pools.
    
First of all depending on the allocation size it is between 3 (1GiB) and
5 (1MiB) times faster than the old implementation.
    
It makes better use of buddy pages to allow for larger physical contiguous
allocations which should result in better TLB utilization at least for amdgpu.
    
Instead of a completely braindead approach of filling the pool with one CPU
while another one is trying to shrink it we only give back freed pages.
    
This also results in much less locking contention and a trylock free MM
shrinker callback, so we can guarantee that pages are given back to the system
when needed.
    
Downside of this is that it takes longer for many small allocations until the
pool is filled up. We could address this, but I couldn't find an use case
where this actually matters. And we don't bother freeing large chunks of pages
any more.
    
The sysfs files are replaced with a single module parameter, allowing users to
override how many pages should be globally pooled in TTM. This unfortunately
breaks the UAPI slightly, but as far as we know nobody ever depended on this.
   
Zeroing memory coming from the pool was handled inconsistently. The
alloc_pages() based pool was zeroing it, the dma_alloc_attr() based one wasn't.
The new implementation isn't zeroing pages from the pool either and only sets
the __GFP_ZERO flag when necessary.
    
The implementation has only 753 lines of code compared to the over 2600 of the
old one, and also allows for saving quite a bunch of code in the drivers since
we don't need specialized handling there any more based on kernel config.
  
Additional to all of that there was a neat bug with IOMMU, coherent DMA
mappings and huge pages which is now fixed in the new code as well.

Please review and comment,
Christian.


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             reply	other threads:[~2020-10-25 15:41 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-25 15:40 Christian König [this message]
2020-10-25 15:40 ` [PATCH 01/13] drm/ttm: nuke ttm_tt_set_(un)populated again Christian König
2020-10-26  4:43   ` Dave Airlie
2020-10-26 13:36   ` Chauhan, Madhav
2020-10-26 13:43     ` Christian König
2020-10-26 19:26       ` Chauhan, Madhav
2020-10-28 11:40         ` Chauhan, Madhav
2020-10-25 15:40 ` [PATCH 02/13] drm/ttm: move swapin out of page alloc backend Christian König
2020-10-25 15:40 ` [PATCH 03/13] drm/ttm: make num_pages uint32_t Christian König
2020-10-25 15:40 ` [PATCH 04/13] drm/ttm: merge ttm_dma_tt back into ttm_tt Christian König
2020-10-25 15:40 ` [PATCH 05/13] drm/ttm: new TT backend allocation pool Christian König
2020-10-25 18:35   ` kernel test robot
2020-10-25 19:01   ` kernel test robot
2020-10-25 19:01   ` [RFC PATCH] drm/ttm: ttm_pool_apply_caching() can be static kernel test robot
2020-10-26  9:56   ` [PATCH 05/13] drm/ttm: new TT backend allocation pool kernel test robot
2020-10-25 15:40 ` [PATCH 06/13] drm/ttm: wire up the new pool as default one Christian König
2020-10-25 15:40 ` [PATCH 07/13] drm/amdgpu: switch to new allocator Christian König
2020-10-25 15:40 ` [PATCH 08/13] drm/radeon: " Christian König
2020-10-25 15:40 ` [PATCH 09/13] drm/nouveau: " Christian König
2020-10-25 15:40 ` [PATCH 10/13] drm/vmwgfx: " Christian König
2020-10-25 15:40 ` [PATCH 11/13] drm/qxl: drop ttm_page_alloc.h include Christian König
2020-10-25 15:40 ` [PATCH 12/13] drm/vram_helpers: " Christian König
2020-10-25 15:41 ` [PATCH 13/13] drm/ttm: nuke old page allocator Christian König
2020-10-26  5:23 ` drm/ttm: new TT backend allocation pool Dave Airlie
2020-10-26 12:01   ` Christian König
2020-10-26 12:15     ` Daniel Vetter
2020-10-26 13:45 ` Huang Rui

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