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authorBen Hutchings <bhutchings@solarflare.com>2013-02-27 16:50:38 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-03-28 12:12:04 -0700
commit46a84dbc74f10d2f855758d809a0b21592bd2b8e (patch)
parent70a3336df60074b29ac3b546d8fccfbcf7831e95 (diff)
sfc: Only use TX push if a single descriptor is to be written
[ Upstream commit fae8563b25f73dc584a07bcda7a82750ff4f7672 ] 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/net/ethernet/sfc/nic.c b/drivers/net/ethernet/sfc/nic.c
index 76f16b74d1aa..578e52a6eff1 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