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Re: [libvirt] [PATCH 0/6 v3] Add blkio cgroup support



Igor Serebryany wrote:
> On Fri, Feb 18, 2011 at 04:12:28PM +0800, Gui Jianfeng wrote:
>> "blkio.weight" is used to control the Minimal Maximal Bandwidth. If you'd like
>> to control Max bandwidth to let your guests become I/O hungery. "blkio.throttle.*"
>> should helps. But these tunables aren't supported by blkiotune for the time being.
>> I'm considering to implement them in the future.
> 
> I'm still a bit confused. The "weight" controls the 'percentage' of
> resources the VM gets compared to other VMs (or other processes
> participating in the cgroup)? If I have 5 processes running on the
> system, and 4 of them are VMs using cgroups, then the VMs get 4/5s of
> all CPU time for IO tasks, and each VM gets an amount of that 4/5th
> proportional to it's weight? Yes?

Yes, if all weight are the same.

> 
> Then, blkio.throttle can be used to set actual hard limits on IO
> consumption -- like, no more than 10Mbps for this VM. I can already do
> this with blkio cgroups, but just not from libvirt -- yes?

yes

> 
> Like many people using libvirt, I only use my hosts for running VMs, and
> I am most interested in limiting IO operations per host to make sure
> that no host monopolizes our SAN. Is there a way for me to just set a
> hard IO throttle limit for libvirt as a whole which would apply to all
> child VMs created by libvirt? I saw a discussion on this list regarding
> group hierarchy, but it went over my head.

There's no way to set this limit by libvirt.
But, I think you can set the limit by hand in cgroup directory. ;)

Thanks,
Gui

> 
> --Igor


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