[libvirt] [PATCH] qemuBuildNicDevStr: Adapt to new advisory on multiqueue

[Martin Kletzander]

On Tue, Mar 04, 2014 at 10:47:38AM +0100, Michal Privoznik wrote:
> As I did previously in 4f588a1b46, libvirt needs to set virtio vectors.
> Previously, we were advised to use vectors=N, where
>
> N = 2 * (number of queues) + 1
>
> However, just recently this advisory has changed on the Multiquue wiki
> page [1] to:
>
> N = 2 * (number of queues) + 2
>
> 1: http://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature
>
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>

ACK

> Notes:
>     I've had some discussion with qemu developers that qemu is the
>     best place to compute sane default [1]. And they agreed with me.
>     However, until they will do so, libvirt should pass the correct
>     value to make the whole feature work correctly.
>
>     1: https://bugzilla.redhat.com/show_bug.cgi?id=1005626
>

I haven't read that, but making sure they'll make the change
introspectable helps us decide whether we need to do that or not.

Martin

>  src/qemu/qemu_command.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index ff0b2d5..18d0a64 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -5036,8 +5036,8 @@ qemuBuildNicDevStr(virDomainDefPtr def,
>      }
>      if (usingVirtio && vhostfdSize > 1) {
>          /* As advised at http://www.linux-kvm.org/page/Multiqueue
> -         * we should add vectors=2*N+1 where N is the vhostfdSize */
> -        virBufferAsprintf(&buf, ",mq=on,vectors=%d", 2 * vhostfdSize + 1);
> +         * we should add vectors=2*N+2 where N is the vhostfdSize */
> +        virBufferAsprintf(&buf, ",mq=on,vectors=%d", 2 * vhostfdSize + 2);
>      }
>      if (vlan == -1)
>          virBufferAsprintf(&buf, ",netdev=host%s", net->info.alias);
> --
> 1.9.0
>
> --
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