From: Willem de Bruijn <will...@google.com>
NAPI tx mode improves TCP behavior by enabling TCP small queues (TSQ).
TSQ reduces queuing ("bufferbloat") and burstiness.
Previous measurements have shown significant improvement for
TCP_STREAM style workloads. Such as those in commit 86a5df1495cc
("Merge branch 'virtio-net-tx-napi'").
There has been uncertainty about smaller possible regressions in
latency due to increased reliance on tx interrupts.
The above results did not show that, nor did I observe this when
rerunning TCP_RR on Linux 5.1 this week on a pair of guests in the
same rack. This may be subject to other settings, notably interrupt
coalescing.
In the unlikely case of regression, we have landed a credible runtime
solution. Ethtool can configure it with -C tx-frames [0|1] as of
commit 0c465be183c7 ("virtio_net: ethtool tx napi configuration").
NAPI tx mode has been the default in Google Container-Optimized OS
(COS) for over half a year, as of release M70 in October 2018,
without any negative reports.
Link: https://marc.info/?l=linux-netdev&m=149305618416472
Link: https://lwn.net/Articles/507065/
Signed-off-by: Willem de Bruijn <will...@google.com>
---
now that we have ethtool support and real production deployment,
it seemed like a good time to revisit this discussion.
---
drivers/net/virtio_net.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0d4115c9e20b..4f3de0ac8b0b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -26,7 +26,7 @@
static int napi_weight = NAPI_POLL_WEIGHT;
module_param(napi_weight, int, 0444);
-static bool csum = true, gso = true, napi_tx;
+static bool csum = true, gso = true, napi_tx = true;
module_param(csum, bool, 0444);
module_param(gso, bool, 0444);
module_param(napi_tx, bool, 0644);
--
2.22.0.rc2.383.gf4fbbf30c2-goog
