Re: [PATCH 1/2] sched: add virt sched domain for the guest

[Liu ping fan]

On Wed, May 23, 2012 at 3:54 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Wed, 2012-05-23 at 14:32 +0800, Liu Ping Fan wrote:
>> From: Liu Ping Fan <pingfank@xxxxxxxxxxxxxxxxxx>
>>
>> The guest's scheduler can not see the numa info on the host and
>> this will result to the following scene:
>> Â Supposing vcpu-a on nodeA, vcpu-b on nodeB, when load balance,
>> the tasks' pull and push between these vcpus will cost more. But
>> unfortunately, currently, the guest is just blind to this.
>>
>> This patch want to export the host numa info to the guest, and help
>> guest to rebuild its sched domain based on host's info.
>
> Hell no, we're not going to export sched domains, if kvm/qemu wants this
> its all in sysfs.
>
> The whole sched_domain stuff is a big enough pain as it is, exporting
> this and making it a sodding API is the worst thing ever.
>
> Whatever brainfart made you think this is needed anyway? sysfs contains
> the host topology, qemu can already create whatever guest topology you
> want (see the -smp and -numa arguments), so what gives?

I think -numa option will be used to emulate the special virtual
machine to customer, and do not necessary map to host topology.
And even we map them exactly with -numa option, the movement of vcpu
threads among host nodes will break the topology initialized by -numa
option.
So give the guest a opportunity to adjust its topology?

Thanks and regards,
pingfan
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