linux-kernel - Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

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Message-ID: <20120608165014.GB27374@one.firstfloor.org>
Date:	Fri, 8 Jun 2012 18:50:14 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, andi@...stfloor.org, mingo@...e.hu,
	ming.m.lin@...el.com, Andreas Herrmann <andreas.herrmann3@....com>,
	Borislav Petkov <borislav.petkov@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

> Why do we have per-cpu firmware anyway?

Consider CPU hotplug.  A newly plugged CPU is not updated yet, but will
be after hotplug.

However i suppose it would be possible to do the update early in the 
boot up sequence before others can use it. That would avoid this problem.

-Andi
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