[PATCH net-next v3] page_pool: check for dma_sync_size earlier

[Furong Xu <0x1207@gmail.com>]

Setting dma_sync_size to 0 is not illegal, fec_main.c and ravb_main.c
already did.
We can save a couple of function calls if check for dma_sync_size earlier.

This is a micro optimization, about 0.6% PPS performance improvement
has been observed on a single Cortex-A53 CPU core with 64 bytes UDP RX
traffic test.

Before this patch:
The average of packets per second is 234026 in one minute.

After this patch:
The average of packets per second is 235537 in one minute.

Signed-off-by: Furong Xu <0x1207@gmail.com>
---
V2 -> V3: Add more details about measurement in commit message
V2: https://lore.kernel.org/r/20250103082814.3850096-1-0x1207@gmail.com

V1 -> V2: Add measurement data about performance improvement in commit message
V1: https://lore.kernel.org/r/20241010114019.1734573-1-0x1207@gmail.com
---
 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 9733206d6406..9bb2d2300d0b 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -458,7 +458,7 @@ page_pool_dma_sync_for_device(const struct page_pool *pool,
 			      netmem_ref netmem,
 			      u32 dma_sync_size)
 {
-	if (pool->dma_sync && dma_dev_need_sync(pool->p.dev))
+	if (pool->dma_sync && dma_dev_need_sync(pool->p.dev) && dma_sync_size)
 		__page_pool_dma_sync_for_device(pool, netmem, dma_sync_size);
 }
 
-- 
2.34.1