Re: [PATCH] perf/x86/intel: Add proper condition to run sched_task callbacks

From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>, Andi Kleen <andi@firstfloor.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Kan Liang <kan.liang@intel.com>
Subject: Re: [PATCH] perf/x86/intel: Add proper condition to run sched_task callbacks
Date: Tue, 18 Jul 2017 11:14:44 +0200	[thread overview]
Message-ID: <20170718091444.afqdtgjijcztv2mn@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170717150156.11784-1-jolsa@kernel.org>

On Mon, Jul 17, 2017 at 05:01:56PM +0200, Jiri Olsa wrote:
> The x86 pmu currently uses the sched_task callback for 2 functions:
>   - PEBS drain
>   - save/restore LBR data
> 
> They are both triggered once the x86 pmu is registered with
> perf_sched_cb_inc call (within pmu::add	callback), regardless
> if there's actually any PEBS or LBR event configured on the cpu.

I don't understand. If we do pmu::add() we _are_ on the CPU.

So you're saying intel_pmu_pebs_{add,del}() are doing it wrong? So why
not fix those?

> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index aa62437d1aa1..1f66356d8122 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3265,9 +3265,11 @@ static void intel_pmu_cpu_dying(int cpu)
>  static void intel_pmu_sched_task(struct perf_event_context *ctx,
>  				 bool sched_in)
>  {
> -	if (x86_pmu.pebs_active)
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +
> +	if (intel_pmu_pebs_needs_sched_cb(cpuc))
>  		intel_pmu_pebs_sched_task(ctx, sched_in);

So I'm confused, if we'd not need this, how come we're here in the first
place?