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From: peterz@infradead.org
To: kan.liang@linux.intel.com
Cc: mingo@redhat.com, acme@kernel.org, linux-kernel@vger.kernel.org,
	ak@linux.intel.com, mark.rutland@arm.com, luto@amacapital.net
Subject: Re: [PATCH V2 3/3] perf/x86: Reset the dirty counter to prevent the leak for an RDPMC task
Date: Tue, 8 Sep 2020 17:58:40 +0200	[thread overview]
Message-ID: <20200908155840.GC35926@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200907160115.GS2674@hirez.programming.kicks-ass.net>

On Mon, Sep 07, 2020 at 06:01:15PM +0200, peterz@infradead.org wrote:
> On Fri, Aug 21, 2020 at 12:57:54PM -0700, kan.liang@linux.intel.com wrote:
> > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> > index 0f3d01562ded..fa08d810dcd2 100644
> > --- a/arch/x86/events/core.c
> > +++ b/arch/x86/events/core.c
> > @@ -1440,7 +1440,10 @@ static void x86_pmu_start(struct perf_event *event, int flags)
> >  
> >  	cpuc->events[idx] = event;
> >  	__set_bit(idx, cpuc->active_mask);
> > -	__set_bit(idx, cpuc->running);
> > +	/* The cpuc->running is only used by the P4 PMU */
> > +	if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON) &&
> > +	    (boot_cpu_data.x86 == 0xf))
> > +		__set_bit(idx, cpuc->running);
> >  	x86_pmu.enable(event);
> >  	perf_event_update_userpage(event);
> >  }
> 
> Yuck! Use a static_branch() or something. This is a gnarly nest of code
> that runs 99.9% of the time to conclude a negative. IOW a complete waste
> of cycles for everybody not running a P4 space heater.

Better still, move it into p4_pmu_enable_event().

  reply	other threads:[~2020-09-08 19:25 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-21 19:57 [PATCH V2 1/3] perf/core: Pull pmu::sched_task() into perf_event_context_sched_in() kan.liang
2020-08-21 19:57 ` [PATCH V2 2/3] perf/core: Pull pmu::sched_task() into perf_event_context_sched_out() kan.liang
2020-09-11  7:02   ` [tip: perf/core] " tip-bot2 for Kan Liang
2020-08-21 19:57 ` [PATCH V2 3/3] perf/x86: Reset the dirty counter to prevent the leak for an RDPMC task kan.liang
2020-09-07 16:01   ` peterz
2020-09-08 15:58     ` peterz [this message]
2020-09-09 13:24     ` Liang, Kan
2020-09-11  7:02 ` [tip: perf/core] perf/core: Pull pmu::sched_task() into perf_event_context_sched_in() tip-bot2 for Kan Liang

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