From: Willem de Bruijn <willemdebruijn.ker...@gmail.com>
Date: Thu, 13 Jun 2019 12:24:57 -0400
> 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>
Applied.
