Re: [PATCH net-next] virtio_net: Disable interrupts if napi_complete_done rescheduled napi

From: Jason Wang <redacted>
Date: Thu, 7 Dec 2017 15:08:45 +0800

On 2017年12月07日 13:09, Michael S. Tsirkin wrote:

quoted

On Thu, Dec 07, 2017 at 01:15:15PM +0900, Toshiaki Makita wrote:

quoted

Since commit 39e6c8208d7b ("net: solve a NAPI race") napi has been
able
to be rescheduled within napi_complete_done() even in non-busypoll
case,
but virtnet_poll() always enabled interrupts before complete, and when
napi was rescheduled within napi_complete_done() it did not disable
interrupts.
This caused more interrupts when event idx is disabled.

According to commit cbdadbbf0c79 ("virtio_net: fix race in RX VQ
processing") we cannot place virtqueue_enable_cb_prepare() after
NAPI_STATE_SCHED is cleared, so disable interrupts again if
napi_complete_done() returned false.

Tested with vhost-user of OVS 2.7 on host, which does not have the
event
idx feature.

...

quoted

quoted

Signed-off-by: Toshiaki Makita <redacted>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

it might make sense in net and not -next since tx napi regressed
performance
in some configs, this might bring it back at least partially.
Jason - what do you think?

No sure, the regression I saw was tested with event idx on. And
virtqueue_disable_cb() does almost nothing for event idx (or even a
little bit slower).

The patch looks good.

Acked-by: Jason Wang <redacted>

I'm going to put this into net-next for now.