linux-kernel - Re: question on sched-rt group allocation cap: sched_rt_runtime

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Message-Id: <729B1E67-339D-405E-A07D-80C8275B55FF@anirban.org>
Date:	Tue, 8 Sep 2009 07:41:01 -0700
From:	Anirban Sinha <ani@...rban.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Anirban Sinha <ASinha@...gmasystems.com>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Dario Faggioli <raistlin@...ux.it>
Subject: Re: question on sched-rt group allocation cap: sched_rt_runtime_us


On 2009-09-08, at 1:42 AM, Peter Zijlstra wrote:

> On Tue, 2009-09-08 at 00:08 -0700, Anirban Sinha wrote:
>
>>> Actually there is, use cpusets to carve the system into partitions.
>>
>> hmm. ok. I looked at the code a little bit. It seems to me that the
>> 'borrowing' of RT runtimes occurs only from rt runqueues belonging to
>> the same root domain. And partition_sched_domains() is the only
>> external interface that can be used to create root domain out of a  
>> CPU
>> set. But then I think it needs to have CGROUPS/USER groups enabled?
>> Right?
>
> No you need cpusets, you create a partition by disabling load- 
> balancing
> on the top set, thereby only allowing load-balancing withing the
> children.
>

Ah I see. Thanks for the clarification.


> The runtime sharing is a form of load-balancing.

sure.


>
> CONFIG_CPUSETS=y


Hmm. Ok. I guess what I meant but did not articulate properly (because  
I was thinking in terms of code) was CPUSETS needed CGROUPS support:

config CPUSETS
	bool "Cpuset support"
	depends on CGROUPS


Anyway, that's fine. I'll dig around the code a little bit more.


>
> Documentation/cgroups/cpusets.txt

Thanks for the pointer. My bad, I did not care to see the docs. I tend  
to ignore docs and read code instead. :D


>

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