Re: [Qemu-discuss] How to use IO throttling and IO burst

[Fam Zheng]

On Thu, 04/03 16:32, Alexandre LAURENT wrote:
> I see, but I am still wondering how "burst" option was thought ? I mean,
> ok, it will not work on local block devices/files since I am starting two
> VMs. Will it work with NFS ? I don't see why it would work better in this
> case.

Would be the same as local block or file. The advantage of IO throttling in
QEMU is it also works with built-in network based backends.

bps_wr_max means the guest can submit its first N bytes without being
throttled.

> Moreover, what are the recommanded options to use with drive to get cgroups
> working ? Is there a need to remove caching or use special caching mode ?

Generally we use cache=none to avoid duplicated page caches in guest, but I
think other cache modes should also work with cgroups limits, though I've not
done this myself.

Thanks,
Fam

> 
> Thank you,
> 
> Best regards,
> 
> Alexandre
> 
> 2014-04-03 11:20 GMT+02:00 Fam Zheng <address@hidden>:
> 
> > On Thu, 04/03 11:06, Alexandre LAURENT wrote:
> > > Hi,
> > >
> > > I am using QEMU 1.7.1 and I would like to know how to use the 'drive'
> > > options :
> > > - bps_wr
> > > - bps_wr_max
> > > - bps_rd
> > > - bps_rd_max
> > >
> > > Can you explain me how to limit IO access between two VMs, where one
> > would
> > > be limited and the second one have full IO access. My point is to give
> > full
> > > IO access to the limited one when the second is doing nothing.
> > >
> >
> > QEMU's block IO throttling cannot do this because one QEMU process doesn't
> > know
> > about other QEMU instances. However if you use local block devices or
> > files as
> > drive backend, it's possible to configure Linux cgroups on two backends
> > with
> > different weights:
> >
> > https://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt
> >
> > Fam
> >