Re: [PATCH 1/2] perf x86: Make intel_pmu_enable_all to enable onlyactive events

[Stephane Eranian]

On Thu, Aug 15, 2013 at 3:53 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> 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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