linux-kernel - Re: [RFC PATCH 2/3 v2] perf: Implement Nehalem uncore pmu

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Date:	Fri, 26 Nov 2010 12:25:51 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Lin Ming <lin@...g.vg>, Lin Ming <ming.m.lin@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC PATCH 2/3 v2] perf: Implement Nehalem uncore pmu

On Fri, Nov 26, 2010 at 12:24 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Fri, 2010-11-26 at 09:18 +0100, Stephane Eranian wrote:
>
>> In the perf_event model, given that any one of the 4 cores can be used
>> to program uncore events, you have no choice but to broadcast to all
>> 4 cores. Each has to demultiplex and figure out which of its counters
>> have overflowed.
>
> Not really, you can redirect all these events to the first online cpu of
> the node.
>
> You can re-write event->cpu in pmu::event_init(), and register cpu
> hotplug notifiers to migrate the state around.
>
I am sure you could. But then the user thinks the event is controlled
from CPUx when it's actually from CPUz. I am sure it can work but
that's confusing, especially interrupt-wise.
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