[PATCH 2/2] drm/ttm: improve uncached page deallocation.

[j.glisse at gmail.com]

From: Jérôme Glisse <jglisse at redhat.com>

Calls to set_memory_wb() incure heavy TLB flush and IPI cost. To
minimize those wait until pool grow beyond batch size before
draining the pool.

Signed-off-by: Jérôme Glisse <jglisse at redhat.com>
Reviewed-by: Mario Kleiner <mario.kleiner.de at gmail.com>
Cc: Michel Dänzer <michel at daenzer.net>
Cc: Thomas Hellstrom <thellstrom at vmware.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
---
 drivers/gpu/drm/ttm/ttm_page_alloc_dma.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
index 0194a93..8028dd6 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
@@ -953,7 +953,12 @@ void ttm_dma_unpopulate(struct ttm_dma_tt *ttm_dma, struct device *dev)
 	} else {
 		pool->npages_free += count;
 		list_splice(&ttm_dma->pages_list, &pool->free_list);
-		if (pool->npages_free > _manager->options.max_size)
+		/*
+		 * Wait to have at at least NUM_PAGES_TO_ALLOC number of pages
+		 * to free in order to minimize calls to set_memory_wb().
+		 */
+		if (pool->npages_free >= (_manager->options.max_size +
+					  NUM_PAGES_TO_ALLOC))
 			npages = pool->npages_free - _manager->options.max_size;
 	}
 	spin_unlock_irqrestore(&pool->lock, irq_flags);
-- 
1.8.3.1