linux-kernel - Re: [PATCH 5/6] perf: Optimise topology iteration

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Date:	Mon, 21 Feb 2011 04:32:35 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...gle.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] perf: Optimise topology iteration

On Mon, Feb 21, 2011 at 11:29:24AM +0800, Lin Ming wrote:
> On Mon, 2011-02-21 at 05:15 +0800, Andi Kleen wrote:
> > On Mon, Feb 21, 2011 at 12:57:39AM +0800, Lin Ming wrote:
> > > Currently we iterate the full machine looking for a matching core_id/nb
> > > for the percore and the amd northbridge stuff , using a smaller topology
> > > mask makes sense.
> > 
> > This is still wrong for CPU hotplug. The CPU "owning" the per core
> > does not necessarily need to be online anymore.
> 
> This is remain issue for hotplug case, no matter we use
> for_each_online_cpu or topology_thread_cpumask.

The original code I submitted used for_each_possible_cpu which
is correct.

> 
> > Please drop this patch.
> 
> Re-look at the code, I think for_each_online_cpu is wrong for percore,
> we should use topology_thread_cpumask instead.

No, that's also cleared on unplug. You really need the possible map
and nothing else.

-Andi
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