Re: virtio-blk performance and MSI

[Avi Kivity <avi@redhat.com>]

On 08/06/2009 07:35 PM, Christoph Hellwig wrote:
> Michael suggested to me a while ago to try MSI with virtio-blk and I
> played with this small patch:
>
>
> Index: qemu-kvm/hw/virtio-blk.c
> ===================================================================
> --- qemu-kvm.orig/hw/virtio-blk.c
> +++ qemu-kvm/hw/virtio-blk.c
> @@ -416,6 +416,7 @@ VirtIODevice *virtio_blk_init(DeviceStat
>       s->vdev.get_config = virtio_blk_update_config;
>       s->vdev.get_features = virtio_blk_get_features;
>       s->vdev.reset = virtio_blk_reset;
> +    s->vdev.nvectors = 2;
>       s->bs = bs;
>       s->rq = NULL;
>       if (strlen(ps = (char *)drive_get_serial(bs)))
>
> which gave about 5% speedups on 4k sized reads and writes, see the full
> iozone output I attached.  Now getting the information about using
> multiple MSI vectors from the command line to virtio-blk similar to how
> virtio-net does seems extremly messy right now.  Waiting for Gerd's
> additional qdev patches to make it easier as a qdev property.
>
>    

Looks good.  Anthony, I think this applies upstream?

-- 
error compiling committee.c: too many arguments to function