[3.5.y.z,extended,stable] Patch "sfc: Only use TX push if a single descriptor is to be written" has been added to staging queue

Message ID 1364234630-10901-1-git-send-email-luis.henriques@canonical.com
State New
Headers show

Commit Message

Luis Henriques March 25, 2013, 6:03 p.m.
This is a note to let you know that I have just added a patch titled

    sfc: Only use TX push if a single descriptor is to be written

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



From 46b30b348c60b83d892c1165ba604f425c0507b4 Mon Sep 17 00:00:00 2001
From: Ben Hutchings <bhutchings@solarflare.com>
Date: Wed, 27 Feb 2013 16:50:38 +0000
Subject: [PATCH] sfc: Only use TX push if a single descriptor is to be written

commit fae8563b25f73dc584a07bcda7a82750ff4f7672 upstream.

Using TX push when notifying the NIC of multiple new descriptors in
the ring will very occasionally cause the TX DMA engine to re-use an
old descriptor.  This can result in a duplicated or partly duplicated
packet (new headers with old data), or an IOMMU page fault.  This does
not happen when the pushed descriptor is the only one written.

TX push also provides little latency benefit when a packet requires
more than one descriptor.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
 drivers/net/ethernet/sfc/nic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)



diff --git a/drivers/net/ethernet/sfc/nic.c b/drivers/net/ethernet/sfc/nic.c
index 76f16b7..578e52a6 100644
--- a/drivers/net/ethernet/sfc/nic.c
+++ b/drivers/net/ethernet/sfc/nic.c
@@ -379,7 +379,8 @@  efx_may_push_tx_desc(struct efx_tx_queue *tx_queue, unsigned int write_count)
 		return false;

 	tx_queue->empty_read_count = 0;
-	return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0;
+	return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0
+		&& tx_queue->write_count - write_count == 1;

 /* For each entry inserted into the software descriptor ring, create a