Subject: Re: [PATCH vhost 21/22] virtio_net: update tx timeout record

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 12 Oct 2023 09:07:23 -0400

On Thu, Oct 12, 2023 at 07:54:02PM +0800, Xuan Zhuo wrote:
> On Thu, 12 Oct 2023 05:36:56 -0400, "Michael S. Tsirkin" <[email-masked]> wrote:
> > On Thu, Oct 12, 2023 at 05:12:33PM +0800, Xuan Zhuo wrote:
> > > On Thu, 12 Oct 2023 05:10:55 -0400, "Michael S. Tsirkin" <[email-masked]> wrote:
> > > > On Wed, Oct 11, 2023 at 05:27:27PM +0800, Xuan Zhuo wrote:
> > > > > If send queue sent some packets, we update the tx timeout
> > > > > record to prevent the tx timeout.
> > > > >
> > > > > Signed-off-by: Xuan Zhuo <[email-masked]>
> > > > > ---
> > > > >  drivers/net/virtio/xsk.c | 10 ++++++++++
> > > > >  1 file changed, 10 insertions(+)
> > > > >
> > > > > diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
> > > > > index 7abd46bb0e3d..e605f860edb6 100644
> > > > > --- a/drivers/net/virtio/xsk.c
> > > > > +++ b/drivers/net/virtio/xsk.c
> > > > > @@ -274,6 +274,16 @@ bool virtnet_xsk_xmit(struct virtnet_sq *sq, struct xsk_buff_pool *pool,
> > > > >
> > > > >  	virtnet_xsk_check_queue(sq);
> > > > >
> > > > > +	if (stats.packets) {
> > > > > +		struct netdev_queue *txq;
> > > > > +		struct virtnet_info *vi;
> > > > > +
> > > > > +		vi = sq->vq->vdev->priv;
> > > > > +
> > > > > +		txq = netdev_get_tx_queue(vi->dev, sq - vi->sq);
> > > > > +		txq_trans_cond_update(txq);
> > > > > +	}
> > > > > +
> > > > >  	u64_stats_update_begin(&sq->stats.syncp);
> > > > >  	sq->stats.packets += stats.packets;
> > > > >  	sq->stats.bytes += stats.bytes;
> > > >
> > > > I don't get what this is doing. Is there some kind of race here you
> > > > are trying to address? And what introduced the race?
> > >
> > >
> > > Because the xsk xmit shares the send queue with the kernel xmit,
> > > then when I do benchmark, the xsk will always use the send queue,
> > > so the kernel may have no chance to do xmit, the tx watchdog
> > > thinks that the send queue is hang and prints tx timeout log.
> > >
> > > So I call the txq_trans_cond_update() to tell the tx watchdog
> > > that the send queue is working.
> > >
> > > Thanks.
> >
> > Don't like this hack.
> > So packets are stuck in queue - that's not good is it?
> > Is ours the only driver that shares queues like this?
> 
> NO.
> 
> And txq_trans_cond_update() is called by many net drivers for the similar reason.
> 
> Thanks

Hmm it seems you are right. OK, sorry about the noise.

> > > > > --
> > > > > 2.32.0.3.g01195cf9f