linux-kernel - Re: [RFC/PATCH 1/4] sched: remove isolcpus

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Date:	Wed, 27 Feb 2008 15:57:20 -0800
From:	Max Krasnyanskiy <maxk@...lcomm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...sign.ru>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Jackson <pj@....com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC/PATCH 1/4] sched: remove isolcpus

Peter Zijlstra wrote:

> cpu isolation doesn't offer anything over cpusets, hence remove it.

Works for me. That's what I suggested in my reply to your comments.
Here is the quote from the previous thread:

>>>> This also allows for isolated groups, there are good reasons to isolate groups,
>>>> esp. now that we have a stronger RT balancer. SMP and hard RT are not
>>>> exclusive. A design that does not take that into account is too rigid.
>> 
>>> You're thinking scheduling only. Paul had the same confusion ;-)
>> 
>> I'm not, I'm thinking it ought to allow for it.
> One way I can think of how to support groups and allow for RT balancer is 
> this: Make scheduler ignore cpu_isolated_map and give cpusets full control of 
> the scheduler domains. Use cpu_isolated_map to only for hw irq and other 
> kernel sub-systems. That way cpusets could mark cpus in the group as isolated 
> to get rid of the  kernel activity and build sched domain such that tasks get 
> balanced in it.
> The thing I do not like about it is that there is no way to boot the system 
> with CPU N isolated from the beginning. Also dynamic isolation currently 
> relies on the cpu hotplug to clear pending irqs, softirqs, kernel timers and 
> threads. So cpusets would have to simulate the cpu hotplug event I guess.

Max

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