On 27 April 2016 at 19:12, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:

> On Wed, 27 Apr 2016 16:39:58 +0200
> Pradeep Kiruvale <pradeepkiruvale@gmail.com> wrote:
>
> > On 27 April 2016 at 10:38, Alberto Garcia <berto@igalia.com> 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.
> >
>
> Indeed.
>
> > 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)*


Thanks,
Pradeep