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 <han...@redhat.com>
> Cc: Michael S. Tsirkin <m...@redhat.com>
> Cc: Neil Horman <nhor...@redhat.com>
> Cc: Jeremy Eder <je...@redhat.com>
> Cc: Marko Myllynen <mylly...@redhat.com>
> Cc: Maxime Coquelin <maxime.coque...@redhat.com>
> Signed-off-by: Jason Wang <jasow...@redhat.com>
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?
> ---
> 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
