Commit 31c03aef authored by Willem de Bruijn's avatar Willem de Bruijn Committed by David S. Miller

virtio_net: enable napi_tx by default

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 86a5df14
("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 0c465be1 ("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: default avatarWillem de Bruijn <willemb@google.com>
Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Acked-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 87f37392
......@@ -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);
......
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