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Re: [libvirt] [PATCH 06/10] vcpubandwidth: introduce two new libvirt APIs




On 07/05/2011 02:06 AM, Wen Congyang wrote:
> At 07/04/2011 07:19 PM, Nikunj A. Dadhania Write:
>> On Thu, 30 Jun 2011 11:13:18 +0800, Wen Congyang <wency cn fujitsu com> wrote:
>>> We want to control bandwidth for each vcpu, so we can not use the
>>> API virDomainSetSchedulerParameters(). Introduce two new APIs to
>>> change and query bandwidth for each vcpu.
>>>
>> Will we have different cpu bandwidth for different vcpus?
>>
>> Something like this:
>>
>> vcpu1: 1000000/250000
>> vcpu2: 1000000/500000
>> vcpu3: 1000000/300000
>> vcpu4: 1000000/400000
>>
>> IMO, that is not required, we can have a top level bandwitdh for the VM
>> and then redistribute it among vcpus equally, without user knowing about
>> it.
>>
>> Something like this:
>>
>> VM1(4vcpu) has to be throttled at 1CPU bandwidth using SetSchedParamters.
>>
>> Internally libvirt splits it equally:
>> vcpu1: 1000000/250000
>> vcpu2: 1000000/250000
>> vcpu3: 1000000/250000
>> vcpu4: 1000000/250000
>>
>> So why introduce VCPU level apis?
> 
> Adam Litke said IBM's performance team nead to control cpu bandwidth for each
> vcpu.
> 

Nikunj is correct here.  We only need to ensure that the bandwidth is
distributed equally between all of the cpus.  This can be accomplished
internally by creating a cgroup for each vcpu and ensuring that
'cpu.share' is the same for each vcpu cgroup.


-- 
Adam Litke
IBM Linux Technology Center


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