linux-kernel - Re: [PATCH v6 03/18] perf/x86: add flags to event constraints

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Date:	Tue, 22 Jan 2013 15:22:43 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH v6 03/18] perf/x86: add flags to event constraints

On Fri, Jan 18, 2013 at 11:59 PM, Andi Kleen <ak@...ux.intel.com> wrote:
>> --- a/arch/x86/kernel/cpu/perf_event_intel.c
>> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
>> @@ -1367,8 +1367,10 @@ x86_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
>>
>>       if (x86_pmu.event_constraints) {
>>               for_each_event_constraint(c, x86_pmu.event_constraints) {
>> -                     if ((event->hw.config & c->cmask) == c->code)
>> +                     if ((event->hw.config & c->cmask) == c->code) {
>> +                             event->hw.flags |= c->flags;
>>                               return c;
>> +                     }
>
> It's not fully clear where that hw.flags field gets initially zeroed. Is that implicit
> in the allocation? Some comments would be good about its live cycle.
>
Yes, this is by allocation.
I used |= in case we need to add more flags in the future.
I will add a comment.

> Or just use a = instead of |=? Why would you have multiple flags in different places?
>
> -Andi
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