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Date: Mon, 13 Jul 2015 14:21:44 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] virtio-blk multiqueue support in qemu.
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Naredula Janardhana Reddy <naredula.jana@gmail.com>, Fam Zheng <famz@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Ming Lei <ming.lei@canonical.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Mon, Jul 13, 2015 at 12:17:43PM +0200, Paolo Bonzini wrote:
> 
> 
> On 09/07/2015 15:29, Michael S. Tsirkin wrote:
> > > On the positive side, we do need something similar to the last 3 patches
> > > to expose multiqueue to the guest.  But it will require much more work
> > > in QEMU to achieve true multiqueue.
> > 
> > Might this be useful as an intermediate step, e.g. for testing
> > guest code?
> 
> Yes, this is already how virtio-scsi multiqueue is implemented.  The
> speedup is noticeable.  However, for virtio-blk there is a huge
> consumption of interrupt vectors in the guest, so it doesn't scale to
> multiple disks as well as virtio-scsi.

Could you elaborate please?  interrupt vector usage is generally
up to the guest, so whatever the issue is might be fixable by driver
changes alone.

-- 
MST