netdev - Re: [PATCH 2/2] virtio_net: Defer skb allocation in receive path

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Message-ID: <20100104211454.GB21488@redhat.com>
Date:	Mon, 4 Jan 2010 23:14:54 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	Amit Shah <amit.shah@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Avi Kivity <avi@...hat.com>, netdev@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH 2/2] virtio_net: Defer skb allocation in receive path

On Mon, Jan 04, 2010 at 01:25:44PM -0800, Shirley Ma wrote:
> Hello Amit,
> 
> Sorry for late response. I am just back from vacation.
> 
> On Thu, 2009-12-24 at 19:07 +0530, Amit Shah wrote:
> > > +static void free_unused_bufs(struct virtnet_info *vi)
> > > +{
> > > +     void *buf;
> > > +     while (vi->num) {
> > > +             buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
> > > +             if (!buf)
> > > +                     continue;
> > 
> > Do you mean 'break' here?
> 
> Nope, it means break since the buffer usage is not sorted by descriptors
> from my understanding. It breaks when vi->num reaches 0.
> 
> Thanks
> Shirley
t

I don't understand.
detach_unused_buf has:
+               if (!vq->data[i])
+                       continue;

so it will never return NULL unless no more buffers?  breaking here ad
BUG_ON(vi->num) as Amit suggests seems cleaner than looping forever if
there's a bug.

-- 
MST
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