On Fri, Nov 25, 2016 at 06:43:08AM +0200, Michael S. Tsirkin wrote:
> On Fri, Nov 25, 2016 at 12:37:26PM +0800, Jason Wang wrote:
> > We use single queue even if multiqueue is enabled and let admin to
> > enable it through ethtool later. This is used to avoid possible
> > regression (small packet TCP stream transmission). But looks like an
> > overkill since:
> >
> > - single queue user can disable multiqueue when launching qemu
> > - brings extra troubles for the management since it needs extra admin
> > tool in guest to enable multiqueue
> > - multiqueue performs much better than single queue in most of the
> > cases
> >
> > So this patch enables multiqueue by default: if #queues is less than or
> > equal to #vcpu, enable as much as queue pairs; if #queues is greater
> > than #vcpu, enable #vcpu queue pairs.
> >
> > Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxx>
> > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > Cc: Neil Horman <nhorman@xxxxxxxxxx>
> > Cc: Jeremy Eder <jeder@xxxxxxxxxx>
> > Cc: Marko Myllynen <myllynen@xxxxxxxxxx>
> > Cc: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
>
> OK at some level but all uses of num_online_cpus()
> like this are racy versus hotplug.
> I know we already have this bug but shouldn't we fix it
> before we add more?
>
Isn't the fix orthogonal to this use though? That is to say, you shoudl
register a hotplug notifier first, and use the handler to adjust the number of
queues on hotplug add/remove?
Neil
>
> > ---
> > drivers/net/virtio_net.c | 9 +++++++--
> > 1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index d4ac7a6..a21d93a 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1886,8 +1886,11 @@ static int virtnet_probe(struct virtio_device *vdev)
> > if (vi->any_header_sg)
> > dev->needed_headroom = vi->hdr_len;
> >
> > - /* Use single tx/rx queue pair as default */
> > - vi->curr_queue_pairs = 1;
> > + /* Enable multiqueue by default */
> > + if (num_online_cpus() >= max_queue_pairs)
> > + vi->curr_queue_pairs = max_queue_pairs;
> > + else
> > + vi->curr_queue_pairs = num_online_cpus();
> > vi->max_queue_pairs = max_queue_pairs;
> >
> > /* Allocate/initialize the rx/tx queues, and invoke find_vqs */
> > @@ -1918,6 +1921,8 @@ static int virtnet_probe(struct virtio_device *vdev)
> > goto free_unregister_netdev;
> > }
> >
> > + virtnet_set_affinity(vi);
> > +
> > /* Assume link up if device can't report link status,
> > otherwise get link status from config. */
> > if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> > --
> > 2.7.4
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