[PATCH net-next 0/2] Some minor optimization for page pool

Patch 1: Use relexed atomic for release side accounting
Patch 2: Minor optimize for page_pool_dma_map() function

Yunsheng Lin (2):
  page_pool: use relexed atomic for release side accounting
  page_pool: optimize the cpu sync operation when DMA mapping

 net/core/page_pool.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

-- 
2.7.4

There is no need to synchronize the account updating, so
use the relexed atomic to avoid some memory barrier in the
data path.

Signed-off-by: Yunsheng Lin <redacted>
---
 net/core/page_pool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index e140905..1a69784 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c

@@ -370,7 +370,7 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
 	/* This may be the last page returned, releasing the pool, so
 	 * it is not safe to reference pool afterwards.
 	 */
-	count = atomic_inc_return(&pool->pages_state_release_cnt);
+	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
 	trace_page_pool_state_release(pool, page, count);
 }
 EXPORT_SYMBOL(page_pool_release_page);

-- 
2.7.4

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 <redacted>
---
 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

On 20.08.2021 04:06, Yunsheng Lin wrote:

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.

This shouldn't be needed. dma_mapping_error() will be (most likely)
inlined by the compiler, and it includes the unlikely() hint.

On 2021/8/20 14:10, Heiner Kallweit wrote:

On 20.08.2021 04:06, Yunsheng Lin wrote:

quoted

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.

This shouldn't be needed. dma_mapping_error() will be (most likely)
inlined by the compiler, and it includes the unlikely() hint.

Good point, will remove the unlikely() mark.
Thanks.

quoted

Signed-off-by: Yunsheng Lin <redacted>
---
 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;
 }
 

.