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Re: [Qemu-discuss] [Qemu-devel] iolimits for virtio-9p

From: Pradeep Kiruvale
Subject: Re: [Qemu-discuss] [Qemu-devel] iolimits for virtio-9p
Date: Thu, 28 Apr 2016 11:45:41 +0200

On 27 April 2016 at 19:12, Greg Kurz <address@hidden> wrote:
On Wed, 27 Apr 2016 16:39:58 +0200
Pradeep Kiruvale <address@hidden> wrote:

> On 27 April 2016 at 10:38, Alberto Garcia <address@hidden> wrote:
> > On Wed, Apr 27, 2016 at 09:29:02AM +0200, Pradeep Kiruvale wrote:
> >
> > > Thanks for the reply. I am still in the early phase, I will let you
> > > know if any changes are needed for the APIs.
> > >
> > > We might also have to implement throttle-group.c for 9p devices, if
> > > we want to apply throttle for group of devices.
> >
> > Fair enough, but again please note that:
> >
> > - throttle-group.c is not meant to be generic, but it's tied to
> >   BlockDriverState / BlockBackend.
> > - it is currently being rewritten:
> >   https://lists.gnu.org/archive/html/qemu-block/2016-04/msg00645.html
> >
> > If you can explain your use case with a bit more detail we can try to
> > see what can be done about it.
> >
> >
> We want to use  virtio-9p for block io instead of virtio-blk-pci. But in
> case of

9p is mostly aimed at sharing files... why would you want to use it for
block io instead of a true block device ? And how would you do that ?

Yes, we want to share the files itself. So we are using the virtio-9p.
We want to have QoS on these files access for every VM.

> virtio-9p we can just use fsdev devices, so we want to apply throttling
> (QoS)
> on these devices and as of now the io throttling only possible with the
> -drive option.


> As a work around we are doing the throttling using cgroup. It has its own
> costs.

Can you elaborate ?

We saw that we need to create cgroups and set it and also we observed lot of iowaits 
compared to implementing the throttling inside the qemu.
This we did observe by using the virtio-blk-pci devices. (Using cgroups Vs qemu throttling)


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