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

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Date:	Thu, 5 May 2011 08:38:19 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.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

"Michael S. Tsirkin" <mst@...hat.com> wrote on 05/05/2011 01:30:23 AM:

> > > @@ -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?

Yes, it is not needed. I will be testing it without this
also.

thanks,

- KK

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