linux-kernel - Re: [CPUISOL] CPU isolation extensions

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Message-ID: <479E20DA.2080403@qualcomm.com>
Date:	Mon, 28 Jan 2008 10:37:14 -0800
From:	Max Krasnyanskiy <maxk@...lcomm.com>
To:	Paul Jackson <pj@....com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, srostedt@...hat.com,
	ghaskins@...ell.com
Subject: Re: [CPUISOL] CPU isolation extensions

Paul Jackson wrote:
> Thanks for the CC, Peter.
> 
>   Ingo - see question at end of message.
> 
> Max wrote:
>> We've had scheduler support for CPU isolation ever since O(1) scheduler went it. 
>> I'd like to extend it further to avoid kernel activity on those CPUs as much as possible.
> 
> I recently added the per-cpuset flag 'sched_load_balance' for some
> other realtime folks, so that they can disable the kernel scheduler
> load balancing on isolated CPUs.  It essentially allows for dynamic
> control of which CPUs are isolated by the scheduler, using the cpuset
> hierarchy, rather than enhancing the 'isolated_cpus' mask.   That
> 'isolated_cpus' mask remained a minimal kernel boottime parameter.
> I believe this went to Linus's tree about Oct 2007.
> 
> It looks like you have three additional tweaks for realtime in this
> patch set, with your patches:
> 
>   [PATCH] [CPUISOL] Do not route IRQs to the CPUs isolated at boot
>   [PATCH] [CPUISOL] Support for workqueue isolation
>   [PATCH] [CPUISOL] Isolated CPUs should be ignored by the "stop machine"
> 
> It would be interesting to see a patchset with the above three realtime
> tweaks, layered on this new cpuset 'sched_load_balance' apparatus, rather
> than layered on changes to make 'isolated_cpus' more dynamic.  Some of us
> run realtime and cpuset-intensive loads on the same system, so like to
> have those two capabilities co-operate with each other.
I'll definitely take a look. So far it seems that extending cpu_isolated_map
is more natural way of propagating this notion to the rest of the kernel.
Since it's very similar to the cpu_online_map concept and it's easy to integrated
with the code that already uses it. 
Anyway. I'll take a look at the cpuset flag that you mentioned and report back.

Thanx
Max
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