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

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Message-ID: <CAFgQCTvhVs8-onz3huovYe=StOYJe2pJO-nka_7KogSju6AttQ@mail.gmail.com>
Date:	Wed, 23 May 2012 16:10:43 +0800
From:	Liu ping fan <kernelfans@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	qemu-devel@...gnu.org, Ingo Molnar <mingo@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [PATCH 1/2] sched: add virt sched domain for the guest

On Wed, May 23, 2012 at 3:54 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, 2012-05-23 at 14:32 +0800, Liu Ping Fan wrote:
>> From: Liu Ping Fan <pingfank@...ux.vnet.ibm.com>
>>
>> The guest's scheduler can not see the numa info on the host and
>> this will result to the following scene:
>>   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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