netdev - Re: [PATCH 2/4] [RFC] virtio: Introduce new API to get free space

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Message-ID: <20110504200023.GA20303@redhat.com>
Date:	Wed, 4 May 2011 23:00:23 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Krishna Kumar <krkumar2@...ibm.com>
Cc:	davem@...emloft.net, eric.dumazet@...il.com, kvm@...r.kernel.org,
	netdev@...r.kernel.org, rusty@...tcorp.com.au
Subject: Re: [PATCH 2/4] [RFC] virtio: Introduce new API to get free space

On Wed, May 04, 2011 at 05:50:19PM +0300, Michael S. Tsirkin wrote:
> > @@ -185,11 +193,6 @@ int virtqueue_add_buf_gfp(struct virtque
> >  	if (vq->num_free < out + in) {
> >  		pr_debug("Can't add buf len %i - avail = %i\n",
> >  			 out + in, vq->num_free);
> > -		/* FIXME: for historical reasons, we force a notify here if
> > -		 * there are outgoing parts to the buffer.  Presumably the
> > -		 * host should service the ring ASAP. */
> > -		if (out)
> > -			vq->notify(&vq->vq);
> >  		END_USE(vq);
> >  		return -ENOSPC;
> >  	}
> 
> This will break qemu versions 0.13 and back.
> I'm adding some new virtio ring flags, we'll be
> able to reuse one of these to mean 'no need for
> work around', I think.

Not really, it wont. We shall almost never get here at all.
But then, why would this help performance?

> -- 
> MST
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