On Thu, Dec 07, 2017 at 01:15:15PM +0900, Toshiaki Makita wrote:
> 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.
>
> * Before patch:
>
> $ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472
> MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET
> Socket Message Elapsed Messages
> Size Size Time Okay Errors Throughput
> bytes bytes secs # # 10^6bits/sec
>
> 212992 1472 60.00 32763206 0 6430.32
> 212992 60.00 23384299 4589.56
>
> Interrupts on guest: 9872369
> Packets/interrupt: 2.37
>
> * After patch
>
> $ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472
> MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET
> Socket Message Elapsed Messages
> Size Size Time Okay Errors Throughput
> bytes bytes secs # # 10^6bits/sec
>
> 212992 1472 60.00 32794646 0 6436.49
> 212992 60.00 32793501 6436.27
>
> Interrupts on guest: 4941299
> Packets/interrupt: 6.64
>
> Signed-off-by: Toshiaki Makita <makita.toshiaki@xxxxxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
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?
> ---
> drivers/net/virtio_net.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 19a985e..c0db48d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -261,9 +261,12 @@ static void virtqueue_napi_complete(struct napi_struct *napi,
> int opaque;
>
> opaque = virtqueue_enable_cb_prepare(vq);
> - if (napi_complete_done(napi, processed) &&
> - unlikely(virtqueue_poll(vq, opaque)))
> - virtqueue_napi_schedule(napi, vq);
> + if (napi_complete_done(napi, processed)) {
> + if (unlikely(virtqueue_poll(vq, opaque)))
> + virtqueue_napi_schedule(napi, vq);
> + } else {
> + virtqueue_disable_cb(vq);
> + }
> }
>
> static void skb_xmit_done(struct virtqueue *vq)
> --
> 1.8.3.1
>
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