From patchwork Tue Mar 26 15:20:36 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [137/150] sfc: Only use TX push if a single descriptor is to be written From: Luis Henriques X-Patchwork-Id: 231396 Message-Id: <1364311249-14454-138-git-send-email-luis.henriques@canonical.com> To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Ben Hutchings Date: Tue, 26 Mar 2013 15:20:36 +0000 3.5.7.9 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Ben Hutchings 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 Signed-off-by: Luis Henriques --- 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