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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 12 Oct 2023 05:36:56 -0400

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?

> > > --
> > > 2.32.0.3.g01195cf9f