linux-kernel - Re: specjbb2005 and aim7 regression with 2.6.32-rc kernels

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Message-ID: <20091109094425.GA26733@in.ibm.com>
Date:	Mon, 9 Nov 2009 15:14:25 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mike Galbraith <efault@....de>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: specjbb2005 and aim7 regression with 2.6.32-rc kernels

On Mon, Nov 09, 2009 at 10:15:04AM +0100, Peter Zijlstra wrote:
> On Mon, 2009-11-09 at 08:09 +0100, Mike Galbraith wrote:
> > +       smp_read_barrier_depends();
> >         cpumask_setall(cpus);
> > +       cpumask_and(cpus, cpus, cpu_online_mask);
> 
> 
> how about: cpumask_copy(cpus, cpu_online_mask); ?
> 
> Also, iirc cpu_online_mask is guaranteed stable when preemption is
> disabled, otherwise you need to use get/put_online_cpus(), an
> rmb_depends() won't do.

preempt_disable() guarantees that any cpus won't go offline, since we
use stop_machine() to take CPUs offline. I don't think it provides cover
against new cpus coming online.

-- 
Thanks and Regards
gautham
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