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Re: [Qemu-devel] virtio-blk multiqueue support in qemu.
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] virtio-blk multiqueue support in qemu. |
Date: |
Mon, 13 Jul 2015 14:41:47 +0300 |
On Mon, Jul 13, 2015 at 01:24:15PM +0200, Paolo Bonzini wrote:
>
>
> On 13/07/2015 13:21, Michael S. Tsirkin wrote:
> > > 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.
>
> Yes, but in practice neither Linux nor Windows (AFAIK) are able to share
> the same vector across multiple MSIs.
>
> Paolo
AFAIK Linux can do this of you pass in IRQF_SHARED.
We just never saw a need to do this before.
Sharing between devices might also work, I think
Amos Kong made it work under qemu, though this relied
on reading ISR when in MSI mode, which is only allowed
in virtio 1 mode.
virtio spec also lets drivers control the mapping from
VQs to MSI vectors. That's portable across OSes.
That one is actually used, at least the Linux drivers support
a mode where all VQs share a single vector.
--
MST
- [Qemu-devel] virtio-blk multiqueue support in qemu., Naredula Janardhana Reddy, 2015/07/01
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Fam Zheng, 2015/07/01
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Michael S. Tsirkin, 2015/07/08
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Stefan Hajnoczi, 2015/07/09
- Message not available
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Michael S. Tsirkin, 2015/07/09
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Naredula Janardhana Reddy, 2015/07/10
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Stefan Hajnoczi, 2015/07/13
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Paolo Bonzini, 2015/07/13
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Michael S. Tsirkin, 2015/07/13
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu., Paolo Bonzini, 2015/07/13
- Re: [Qemu-devel] virtio-blk multiqueue support in qemu.,
Michael S. Tsirkin <=