GPUs typically benefit from contiguous memory via reduced TLB pressure and improved caching performance, where the maximum size of contiguous block which adds a performance benefit is related to hardware design.
TTM pool allocator by default tries (hard) to allocate up to the system MAX_PAGE_ORDER blocks. This varies by the CPU platform and can also be configured via Kconfig. If that limit was set to be higher than the GPU can make an extra use of, lets allow the individual drivers to let TTM know over which allocation order can the pool allocator afford to make a little bit less effort with. We implement this by disabling direct reclaim for those allocations, which reduces the allocation latency and lowers the demands on the page allocator, in cases where expending this effort is not critical for the GPU in question. Signed-off-by: Tvrtko Ursulin <[email protected]> Cc: Christian König <[email protected]> Cc: Thadeu Lima de Souza Cascardo <[email protected]> Reviewed-by: Christian König <[email protected]> # v1 --- v2: * Rebase for rename and move of flags to alloc_flags / TTM_ALLOCATION_. --- drivers/gpu/drm/ttm/ttm_pool.c | 8 ++++++++ drivers/gpu/drm/ttm/ttm_pool_internal.h | 5 +++++ include/drm/ttm/ttm_allocation.h | 5 +++-- 3 files changed, 16 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c index 4fc69447060c..97e9ce505cf6 100644 --- a/drivers/gpu/drm/ttm/ttm_pool.c +++ b/drivers/gpu/drm/ttm/ttm_pool.c @@ -136,6 +136,7 @@ static DECLARE_RWSEM(pool_shrink_rwsem); static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags, unsigned int order) { + const unsigned int beneficial_order = ttm_pool_beneficial_order(pool); unsigned long attr = DMA_ATTR_FORCE_CONTIGUOUS; struct ttm_pool_dma *dma; struct page *p; @@ -149,6 +150,13 @@ static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags, gfp_flags |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN | __GFP_THISNODE; + /* + * Do not add latency to the allocation path for allocations orders + * device tolds us do not bring them additional performance gains. + */ + if (beneficial_order && order > beneficial_order) + gfp_flags &= ~__GFP_DIRECT_RECLAIM; + if (!ttm_pool_uses_dma_alloc(pool)) { p = alloc_pages_node(pool->nid, gfp_flags, order); if (p) diff --git a/drivers/gpu/drm/ttm/ttm_pool_internal.h b/drivers/gpu/drm/ttm/ttm_pool_internal.h index 96b7f21514fb..82c4b7e56a99 100644 --- a/drivers/gpu/drm/ttm/ttm_pool_internal.h +++ b/drivers/gpu/drm/ttm/ttm_pool_internal.h @@ -17,4 +17,9 @@ static inline bool ttm_pool_uses_dma32(struct ttm_pool *pool) return pool->alloc_flags & TTM_ALLOCATION_POOL_USE_DMA32; } +static inline bool ttm_pool_beneficial_order(struct ttm_pool *pool) +{ + return pool->alloc_flags & 0xff; +} + #endif diff --git a/include/drm/ttm/ttm_allocation.h b/include/drm/ttm/ttm_allocation.h index 7869dc32bd91..8f8544760306 100644 --- a/include/drm/ttm/ttm_allocation.h +++ b/include/drm/ttm/ttm_allocation.h @@ -4,7 +4,8 @@ #ifndef _TTM_ALLOCATION_H_ #define _TTM_ALLOCATION_H_ -#define TTM_ALLOCATION_POOL_USE_DMA_ALLOC BIT(0) /* Use coherent DMA allocations. */ -#define TTM_ALLOCATION_POOL_USE_DMA32 BIT(1) /* Use GFP_DMA32 allocations. */ +#define TTM_ALLOCATION_POOL_BENEFICIAL_ORDER(n) ((n) & 0xff) /* Max order which caller can benefit from */ +#define TTM_ALLOCATION_POOL_USE_DMA_ALLOC BIT(8) /* Use coherent DMA allocations. */ +#define TTM_ALLOCATION_POOL_USE_DMA32 BIT(9) /* Use GFP_DMA32 allocations. */ #endif -- 2.48.0
