linux-kernel - Re: [RFC PATCH 02/10] smp, cpu hotplug: Fix smp_call_function

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Message-ID: <50BF41A4.8010709@linux.vnet.ibm.com>
Date:	Wed, 05 Dec 2012 18:14:20 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	tglx@...utronix.de, peterz@...radead.org,
	paulmck@...ux.vnet.ibm.com, mingo@...nel.org,
	akpm@...ux-foundation.org, namhyung@...nel.org,
	vincent.guittot@...aro.org, sbw@....edu, tj@...nel.org,
	amit.kucheria@...aro.org, rostedt@...dmis.org, rjw@...k.pl,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 02/10] smp, cpu hotplug: Fix smp_call_function_*()
 to prevent CPU offline properly

On 12/05/2012 05:09 AM, Rusty Russell wrote:
> "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> writes:
>> From: Michael Wang <wangyun@...ux.vnet.ibm.com>
>>
>> With stop_machine() gone from the CPU offline path, we can't depend on
>> preempt_disable() to prevent CPUs from going offline from under us.
> 
> Minor gripe: I'd prefer this paragraph to use the future rather than
> past tense, like: "Once stop_machine() is gone ... we won't be able to
> depend".
> 

Fixed in the new version.

> Since you're not supposed to use the _stable() accessors without calling
> get_online_cpus_stable_atomic(), why not have
> get_online_cpus_stable_atomic() return a pointer to the stable cpumask?
> (Which is otherwise static, at least for debug).
>

We don't have to worry about this now because the new version doesn't
use stable cpumask.
 
> Might make the patches messier though...
> 
> Oh, and I'd love to see actual benchmarks to make sure we've actually
> fixed a problem with this ;)
> 

Of course :-) They will follow, once we have a proper implementation
that we are happy with :-)

Regards,
Srivatsa S. Bhat

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