On Sun, Nov 30, 2014 at 11:27:48AM -0800, Eric Dumazet wrote:

On Sun, 2014-11-30 at 10:43 +0800, Wei Yang wrote:

quoted

In commit 6a4e812 (net/mlx4_en: Avoid calling bswap in tx fast path), we store
doorbell_qpn in big endian to avoid bswap(). Then we try to write it directly
by iowrite32() instead of iowrite32be().

This works fine on little endian platform, while has some problem on big
endian platform. Here is the definition in general:

	#define iowrite32(v, addr)	writel((v), (addr))
	#define writel(b,addr)		__raw_writel(__cpu_to_le32(b),addr)

Oh well...

quoted

On little endian platform, the value is not swapped before write. While on big
endian platform, the value is swapped. This is not expected to happen.

This patch does the swap on big endian platform before it is written.

Signed-off-by: Wei Yang <redacted>
CC: Eric Dumazet <edumazet@google.com>
CC: Amir Vadai <redacted>
---
 drivers/net/ethernet/mellanox/mlx4/en_tx.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index 454d9fe..76f028b 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c

@@ -954,7 +954,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
 		tx_desc->ctrl.owner_opcode = op_own;
 		if (send_doorbell) {
 			wmb();
-			iowrite32(ring->doorbell_qpn,
+			iowrite32(__cpu_to_le32(ring->doorbell_qpn),
 				  ring->bf.uar->map + MLX4_SEND_DOORBELL);
 		} else {
 			ring->xmit_more++;

Well, whole idea of the patch was to perform the swap (if any) out of
the fast path.

Yes, I know the it.

ring->doorbell_qpn is a cache of whatever value.

Have you tried to convert it to a __le32 instead of __be32 ?

You mean change the type of doorbell_qpn or the function __cpu_to_be32()?
I don't get your point.

Thanks

-- 
Richard Yang
Help you, Help me