linux-kernel - Re: [RFC] perf_events: support for uncore a.k.a. nest units

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Date:	Thu, 21 Jan 2010 09:59:04 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@...il.com
Cc:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Paul Mackerras <paulus@...ba.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	Philip Mucci <mucci@...s.utk.edu>,
	Maynard Johnson <mpjohn@...ibm.com>, Carl Love <cel@...ibm.com>
Subject: Re: [RFC] perf_events: support for uncore a.k.a. nest units

On Thu, 2010-01-21 at 09:47 +0100, stephane eranian wrote:
> I don't think that is correct. You can be using the uncore PMU on Nehalem
> without any core PMU event. The only thing to realize is that uncore PMU
> shares the same interrupt vector as core PMU. You need to configure which
> core the uncore is going to interrupt on. This is done via a bitmask, so you
> can interrupt more than one core at a time. Several strategies are possible.

Ah, sharing the IRQ line is no problem. But from reading I got the
impression you need to configure an Offcore counter. See 30.6.2.1:

• EN_PMI_COREn (bit n, n = 0, 3 if four cores are present): When set, processor
core n is programmed to receive an interrupt signal from any interrupt enabled
uncore counter. PMI delivery due to an uncore counter overflow is enabled by
setting IA32_DEBUG_CTL.Offcore_PMI_EN to 1.

Which seems to indicate a link with the off-core response thing.

However I would be very glad to be wrong :-)

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