On Wed, Oct 28, 2015 at 11:13:39AM +0800, Jason Wang wrote:
>
>
> On 10/27/2015 04:38 PM, Michael S. Tsirkin wrote:
> > On Mon, Oct 26, 2015 at 10:52:47AM -0700, Ravi Kerur wrote:
> >> Ported earlier patch from Jason Wang (dated 12/26/2014).
> >>
> >> This patch tries to reduce the number of MSIX irqs required for
> >> virtio-net by sharing a MSIX irq for each TX/RX queue pair through
> >> channels. If transport support channel, about half of the MSIX irqs
> >> were reduced.
> >>
> >> Signed-off-by: Ravi Kerur <rke...@gmail.com>
> > Why bother BTW?
>
> The reason is we want to save the number of interrupt vectors used.
> Booting a guest with 256 queues with current driver will result all
> tx/rx queues shares a single vector. This is suboptimal.
With a single CPU? But what configures so many queues? Why do it?
> With this
> series, half could be saved.
At cost of e.g. inability to balance the interrupts.
> And more complex policy could be applied on
> top (e.g limit the number of vectors used by driver).
If that's the motivation, I'd like to see a draft of that more complex
policy first.
> > Looks like this is adding a bunch of overhead
> > on data path - to what end?
>
> I agree some benchmark is needed for this.
>
> > Maybe you have a huge number of these devices ... but in that case, how
> > about sharing the config interrupt instead?
> > That's only possible if host supports VIRTIO_1
> > (so we can detect config interrupt by reading the ISR).
> >
> >
> >
> >> ---
> >> drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
> >> 1 file changed, 28 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> >> index d8838ded..d705cce 100644
> >> --- a/drivers/net/virtio_net.c
> >> +++ b/drivers/net/virtio_net.c
> >> @@ -72,6 +72,9 @@ struct send_queue {
> >>
> >> /* Name of the send queue: output.$index */
> >> char name[40];
> >> +
> >> + /* Name of the channel, shared with irq. */
> >> + char channel_name[40];
> >> };
> >>
> >> /* Internal representation of a receive virtqueue */
> >> @@ -1529,6 +1532,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >> int ret = -ENOMEM;
> >> int i, total_vqs;
> >> const char **names;
> >> + const char **channel_names;
> >> + unsigned *channels;
> >>
> >> /* We expect 1 RX virtqueue followed by 1 TX virtqueue, followed by
> >> * possible N-1 RX/TX queue pairs used in multiqueue mode, followed by
> >> @@ -1548,6 +1553,17 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >> if (!names)
> >> goto err_names;
> >>
> >> + channel_names = kmalloc_array(vi->max_queue_pairs,
> >> + sizeof(*channel_names),
> >> + GFP_KERNEL);
> >> + if (!channel_names)
> >> + goto err_channel_names;
> >> +
> >> + channels = kmalloc_array(total_vqs, sizeof(*channels),
> >> + GFP_KERNEL);
> >> + if (!channels)
> >> + goto err_channels;
> >> +
> >> /* Parameters for control virtqueue, if any */
> >> if (vi->has_cvq) {
> >> callbacks[total_vqs - 1] = NULL;
> >> @@ -1562,10 +1578,15 @@ static int virtnet_find_vqs(struct virtnet_info
> >> *vi)
> >> sprintf(vi->sq[i].name, "output.%d", i);
> >> names[rxq2vq(i)] = vi->rq[i].name;
> >> names[txq2vq(i)] = vi->sq[i].name;
> >> + sprintf(vi->sq[i].channel_name, "txrx.%d", i);
> >> + channel_names[i] = vi->sq[i].channel_name;
> >> + channels[rxq2vq(i)] = i;
> >> + channels[txq2vq(i)] = i;
> >> }
> >>
> >> ret = vi->vdev->config->find_vqs(vi->vdev, total_vqs, vqs, callbacks,
> >> - names);
> >> + names, channels, channel_names,
> >> + vi->max_queue_pairs);
> >> if (ret)
> >> goto err_find;
> >>
> >> @@ -1580,6 +1601,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >> vi->sq[i].vq = vqs[txq2vq(i)];
> >> }
> >>
> >> + kfree(channels);
> >> + kfree(channel_names);
> >> kfree(names);
> >> kfree(callbacks);
> >> kfree(vqs);
> >> @@ -1587,6 +1610,10 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >> return 0;
> >>
> >> err_find:
> >> + kfree(channels);
> >> +err_channels:
> >> + kfree(channel_names);
> >> +err_channel_names:
> >> kfree(names);
> >> err_names:
> >> kfree(callbacks);
> >> --
> >> 1.9.1
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