Commit 7e9c548d authored by Tvrtko Ursulin's avatar Tvrtko Ursulin Committed by Tvrtko Ursulin
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drm/ttm: Allow drivers to specify maximum beneficial TTM pool size 



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: default avatarTvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarTvrtko Ursulin <tursulin@ursulin.net>
Link: https://lore.kernel.org/r/20251020115411.36818-5-tvrtko.ursulin@igalia.com
parent 77e19f8d

drivers/gpu/drm/ttm/ttm_pool.c

+8 −0
Original line number Diff line number Diff line
@@ -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)

drivers/gpu/drm/ttm/ttm_pool_internal.h

+5 −0
Original line number Diff line number Diff line
@@ -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

include/drm/ttm/ttm_allocation.h

+3 −2
Original line number Diff line number Diff line
@@ -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