linux-kernel - [PATCH net-next 2/2] page_pool: optimize the cpu sync operation when DMA mapping

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Date:   Fri, 20 Aug 2021 10:06:35 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     <davem@...emloft.net>, <kuba@...nel.org>
CC:     <hawk@...nel.org>, <ilias.apalodimas@...aro.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH net-next 2/2] page_pool: optimize the cpu sync operation when DMA mapping

If the DMA_ATTR_SKIP_CPU_SYNC is not set, cpu syncing is
also done in dma_map_page_attrs(), so set the attrs according
to pool->p.flags to avoid calling dma sync function again.

Also mark the dma error as the unlikely case While we are at
it.

Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
---
 net/core/page_pool.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 1a69784..8172045 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -191,8 +191,12 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
 
 static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 {
+	unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
 	dma_addr_t dma;
 
+	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
+		attrs = 0;
+
 	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
 	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
 	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
@@ -200,15 +204,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 	 */
 	dma = dma_map_page_attrs(pool->p.dev, page, 0,
 				 (PAGE_SIZE << pool->p.order),
-				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
-	if (dma_mapping_error(pool->p.dev, dma))
+				 pool->p.dma_dir, attrs);
+	if (unlikely(dma_mapping_error(pool->p.dev, dma)))
 		return false;
 
 	page_pool_set_dma_addr(page, dma);
 
-	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
-		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
-
 	return true;
 }
 
-- 
2.7.4