netdev - Re: [rfc net-next v6 2/3] virtio

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Message-ID: <20121118091354.GA31775@redhat.com>
Date:	Sun, 18 Nov 2012 11:13:54 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Jason Wang <jasowang@...hat.com>, davem@...emloft.net,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	krkumar2@...ibm.com, kvm@...r.kernel.org, edumazet@...gle.com
Subject: Re: [rfc net-next v6 2/3] virtio_net: multiqueue support

On Sat, Nov 17, 2012 at 12:35:29AM +0000, Ben Hutchings wrote:
> On Tue, 2012-11-13 at 08:40 +0200, Michael S. Tsirkin wrote:
> > On Mon, Nov 05, 2012 at 11:38:39AM +1030, Rusty Russell wrote:
> > > > @@ -924,11 +1032,10 @@ static void virtnet_get_ringparam(struct net_device *dev,
> > > >  {
> > > >  	struct virtnet_info *vi = netdev_priv(dev);
> > > >  
> > > > -	ring->rx_max_pending = virtqueue_get_vring_size(vi->rvq);
> > > > -	ring->tx_max_pending = virtqueue_get_vring_size(vi->svq);
> > > > +	ring->rx_max_pending = virtqueue_get_vring_size(vi->rq[0].vq);
> > > > +	ring->tx_max_pending = virtqueue_get_vring_size(vi->sq[0].vq);
> > > >  	ring->rx_pending = ring->rx_max_pending;
> > > >  	ring->tx_pending = ring->tx_max_pending;
> > > > -
> > > >  }
> > > 
> > > This assumes all vqs are the same size.  I think this should probably
> > > check: for mq mode, use the first vq, otherewise use the 0th.
> > 
> > For rx_pending/tx_pending I think what is required here is the
> > actual number of outstanding buffers.
> > Dave, Eric - right?
> > 
> > So this should be the total over all rings and to be useful,
> > rx_max_pending/tx_max_pending should be the total too.
> 
> So far as I know, all current implementations use the number of
> descriptors per ring here. virtio_net should be consistent with this.
> 
> Ben.

Problem is, it could in theory be different between rings. I guess we
could use the maximum.

What's the right thing to do for rx_pending - I am guessing
we want the current outstanding packets right?


> > > For bonus points, check this assertion at probe time.
> > 
> > Looks like we can easily support different queues too.
> > 
> 
> -- 
> Ben Hutchings, Staff Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
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