linux-kernel - Re: [PATCH 0/4] CPU hotplug, cpusets: Fix CPU online handling related to cpusets

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Message-ID: <4F35EE11.5010202@linux.vnet.ibm.com>
Date:	Sat, 11 Feb 2012 09:56:57 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	paulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...e.hu>,
	paul@...lmenage.org, tj@...nel.org, frank.rowand@...sony.com,
	pjt@...gle.com, tglx@...utronix.de, lizf@...fujitsu.com,
	prashanth@...ux.vnet.ibm.com, vatsa@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/4] CPU hotplug, cpusets: Fix CPU online handling related
 to cpusets

On 02/11/2012 07:37 AM, Peter Zijlstra wrote:

> On Fri, 2012-02-10 at 23:39 +0100, Rafael J. Wysocki wrote:
>>
>>> I don't see why not.  Presumably no CPUs will be added or removed while 
>>> the system is asleep.
>>
>> ACPI explicitly forbids that level of hardware reconfiguration in a sleep
>> state (even in S4), AFAICS.  Still, people may try to do that ... 
> 
> I'm ok with breaking that :-) If its really really important to someone
> we (him most likely) could fix it by detecting the topology changed over
> the suspend and do a fixup. Assuming it actually gets that far.
> 
> Srivatsa, wanna give this (the proposal to not modify cpusets on
> CPU_TASKS_FROZEN) a try?
> 


Sure! After you pointed out that CPU Hotplug is destructive in general and
hence it is not a good idea to put back online CPUs to cpusets, the next
thing I thought of trying was a special case handling for suspend/resume
alone, IOW, not calling the cpuset update upon CPU_TASKS_FROZEN.

So, yes, I'll write up a patch for that and post it soon :-)

Regards,
Srivatsa S. Bhat

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