linux-kernel - [PATCH net] net: fec: change the default rx copybreak length to 1518

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Date:   Fri, 19 Aug 2022 17:00:41 +0800
From:   wei.fang@....com
To:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net] net: fec: change the default rx copybreak length to 1518

From: Wei Fang <wei.fang@....com>

Set the default rx copybreak value to 1518 so that improve the
performance when SMMU is enabled. User can change the copybreak
length in dynamically by ethtool.

Signed-off-by: Wei Fang <wei.fang@....com>
---
 drivers/net/ethernet/freescale/fec_main.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index e8e2aa1e7f01..f5f34cdba131 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -299,7 +299,15 @@ MODULE_PARM_DESC(macaddr, "FEC Ethernet MAC address");
 #define FEC_WOL_FLAG_ENABLE		(0x1 << 1)
 #define FEC_WOL_FLAG_SLEEP_ON		(0x1 << 2)
 
-#define COPYBREAK_DEFAULT	256
+/* By default, set the copybreak to 1518,
+ * then the RX path always keep DMA memory unchanged, and
+ * allocate one new skb and copy DMA memory data to the new skb
+ * buffer, which can improve the performance when SMMU is enabled.
+ *
+ * The driver support .set_tunable() interface for ethtool, user
+ * can dynamicly change the copybreak value.
+ */
+#define COPYBREAK_DEFAULT	1518
 
 /* Max number of allowed TCP segments for software TSO */
 #define FEC_MAX_TSO_SEGS	100
-- 
2.25.1