Re: [Qemu-devel] [RFC]QEMU disk I/O limits

[Daniel P. Berrange]

On Tue, May 31, 2011 at 09:45:37AM -0400, Vivek Goyal wrote:
> On Mon, May 30, 2011 at 01:09:23PM +0800, Zhi Yong Wu wrote:
> > Hello, all,
> > 
> >     I have prepared to work on a feature called "Disk I/O limits" for 
> > qemu-kvm projeect.
> >     This feature will enable the user to cap disk I/O amount performed by a 
> > VM.It is important for some storage resources to be shared among multi-VMs. 
> > As you've known, if some of VMs are doing excessive disk I/O, they will 
> > hurt the performance of other VMs.
> > 
> 
> Hi Zhiyong,
> 
> Why not use kernel blkio controller for this and why reinvent the wheel
> and implement the feature again in qemu?

The finest level of granularity offered by cgroups apply limits per QEMU
process. So the blkio controller can't be used to apply controls directly
to individual disks used by QEMU, only the VM as a whole.

We networking we can use 'net_cls' cgroups controller for the process
as a whole, or attach  'tc' to individual TAP devices for per-NIC
throttling, both of which ultimately use the same kernel functionality.
I don't see an equivalent option for throttling individual disks that
would reuse functionality from the blkio controller.

Regards,
Daniel
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