linux-kernel - [PATCH net-next v2 1/2] net: mvneta: avoid getting status from rx

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Date:   Fri, 17 Feb 2017 18:02:32 +0800
From:   Jisheng Zhang <jszhang@...vell.com>
To:     <thomas.petazzoni@...e-electrons.com>, <davem@...emloft.net>,
        <arnd@...db.de>
CC:     <linux-arm-kernel@...ts.infradead.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Jisheng Zhang <jszhang@...vell.com>
Subject: [PATCH net-next v2 1/2] net: mvneta: avoid getting status from rx_desc as much as possible

In hot code path mvneta_rx_hwbm(), the rx_desc->status is read twice.
The rx_desc is allocated by dma_alloc_coherent, it's uncacheable if
the device isn't cache-coherent, reading from uncached memory is
fairly slow. So reuse the read out rx_status to avoid the second
reading from uncached memory.

Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
Suggested-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/net/ethernet/marvell/mvneta.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 61dd4462411c..06df72b8da85 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -313,8 +313,8 @@
 	((addr >= txq->tso_hdrs_phys) && \
 	 (addr < txq->tso_hdrs_phys + txq->size * TSO_HEADER_SIZE))
 
-#define MVNETA_RX_GET_BM_POOL_ID(rxd) \
-	(((rxd)->status & MVNETA_RXD_BM_POOL_MASK) >> MVNETA_RXD_BM_POOL_SHIFT)
+#define MVNETA_RX_GET_BM_POOL_ID(status) \
+	(((status) & MVNETA_RXD_BM_POOL_MASK) >> MVNETA_RXD_BM_POOL_SHIFT)
 
 struct mvneta_statistic {
 	unsigned short offset;
@@ -1900,7 +1900,7 @@ static void mvneta_rxq_drop_pkts(struct mvneta_port *pp,
 		for (i = 0; i < rx_done; i++) {
 			struct mvneta_rx_desc *rx_desc =
 						  mvneta_rxq_next_desc_get(rxq);
-			u8 pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_desc);
+			u8 pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_desc->status);
 			struct mvneta_bm_pool *bm_pool;
 
 			bm_pool = &pp->bm_priv->bm_pools[pool_id];
@@ -2075,7 +2075,7 @@ static int mvneta_rx_hwbm(struct mvneta_port *pp, int rx_todo,
 		rx_bytes = rx_desc->data_size - (ETH_FCS_LEN + MVNETA_MH_SIZE);
 		data = (u8 *)(uintptr_t)rx_desc->buf_cookie;
 		phys_addr = rx_desc->buf_phys_addr;
-		pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_desc);
+		pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_status);
 		bm_pool = &pp->bm_priv->bm_pools[pool_id];
 
 		if (!mvneta_rxq_desc_is_first_last(rx_status) ||
-- 
2.11.0