netdev - [PATCH net-next] mvpp2: prefetch frame header

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Date:   Tue, 22 Oct 2019 16:14:38 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Stefan Chulski <stefanc@...vell.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next] mvpp2: prefetch frame header

When receiving traffic, eth_type_trans() is high up on the perf top list,
because it's the first function which access the packet data.

Move the DMA unmap a bit higher, and put a prefetch just after it, so we
have more time to load the data into the cache.

The packet rate increase is about 13% with a tc drop test: 1620 => 1830 kpps

Signed-off-by: Matteo Croce <mcroce@...hat.com>
---
 drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index 111b3b8239e1..17378e0d8da1 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -2966,6 +2966,11 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
 			continue;
 		}
 
+		dma_unmap_single(dev->dev.parent, dma_addr,
+				 bm_pool->buf_size, DMA_FROM_DEVICE);
+
+		prefetch(data);
+
 		if (bm_pool->frag_size > PAGE_SIZE)
 			frag_size = 0;
 		else
@@ -2983,9 +2988,6 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
 			goto err_drop_frame;
 		}
 
-		dma_unmap_single(dev->dev.parent, dma_addr,
-				 bm_pool->buf_size, DMA_FROM_DEVICE);
-
 		rcvd_pkts++;
 		rcvd_bytes += rx_bytes;
 
-- 
2.21.0