linux-kernel - Re: [PATCH 1/2] perf x86: Make intel_pmu_enable

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Message-ID: <CABPqkBQAnj+tNBpQ+ebjTTe2Ht1__w9HzZnB15QGc+czCaYULg@mail.gmail.com>
Date:	Mon, 19 Aug 2013 11:16:54 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 1/2] perf x86: Make intel_pmu_enable_all to enable only
 active events

On Thu, Aug 15, 2013 at 3:53 PM, Andi Kleen <andi@...stfloor.org> wrote:
>>
>> I think its a NOP; this is the global ctrl register but
>> intel_pmu_disable_event() writes PERFEVTSELx.EN = 0, so even if you
>> enable it in the global mask, the event should still be disabled.
>
> Yes the hardware ANDs the various enable bits in the different
> registers.
>
Andi is correct. There is a logical AND between GLOBAL_CTRL and
the individual PERFEVTCTL.EN bits. If the EN bit is zero, then the
counter does not count. That also applies to fixed counters.
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