linux-kernel - Re: [PATCH] perf/x86/intel: Add proper condition to run sched

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Date:   Wed, 19 Jul 2017 00:11:38 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andi Kleen <andi@...stfloor.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>
Subject: Re: [PATCH] perf/x86/intel: Add proper condition to run sched_task
 callbacks

On Tue, Jul 18, 2017 at 02:37:34PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 18, 2017 at 11:29:32AM +0200, Jiri Olsa wrote:
> 
> > because we have 2 places using the same callback
> >   - PEBS drain for free running counters
> >   - LBR save/store
> > 
> > both of them called from intel_pmu_sched_task
> > 
> > so let's say PEBS drain setup the callback for the event,
> > but in the callback itself (intel_pmu_sched_task) we will
> > also run the code for LBR save/restore, which we did not
> > ask for, but the code in intel_pmu_sched_task does not
> > check for that
> 
> Ah fair enough; Changelog confused me.
> 
> > I'm adding conditions to recognize the work that needs
> > to be done in the callback
> > 
> > another option might be to add support for more x86_pmu::sched_task
> > callbacks, which might be cleaner
> 
> Right; either that or pull the condition into the functions themselves
> to create less churn. Something like so I suppose...

ok, will send new version

jirka

> 
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index aa62437d1aa1..2d533d4c0e2c 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3265,10 +3265,8 @@ 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)
> -		intel_pmu_pebs_sched_task(ctx, sched_in);
> -	if (x86_pmu.lbr_nr)
> -		intel_pmu_lbr_sched_task(ctx, sched_in);
> +	intel_pmu_pebs_sched_task(ctx, sched_in);
> +	intel_pmu_lbr_sched_task(ctx, sched_in);
>  }
>  
>  PMU_FORMAT_ATTR(offcore_rsp, "config1:0-63");
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index c6d23ffe422d..6ee7ebdc8555 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -606,12 +606,6 @@ static inline void intel_pmu_drain_pebs_buffer(void)
>  	x86_pmu.drain_pebs(&regs);
>  }
>  
> -void intel_pmu_pebs_sched_task(struct perf_event_context *ctx, bool sched_in)
> -{
> -	if (!sched_in)
> -		intel_pmu_drain_pebs_buffer();
> -}
> -
>  /*
>   * PEBS
>   */
> @@ -816,6 +810,14 @@ static inline bool pebs_needs_sched_cb(struct cpu_hw_events *cpuc)
>  	return cpuc->n_pebs && (cpuc->n_pebs == cpuc->n_large_pebs);
>  }
>  
> +void intel_pmu_pebs_sched_task(struct perf_event_context *ctx, bool sched_in)
> +{
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +
> +	if (!sched_in && pebs_needs_sched_cb(cpuc))
> +		intel_pmu_drain_pebs_buffer();
> +}
> +
>  static inline void pebs_update_threshold(struct cpu_hw_events *cpuc)
>  {
>  	struct debug_store *ds = cpuc->ds;
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index eb261656a320..955457a30197 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -380,8 +380,12 @@ static void __intel_pmu_lbr_save(struct x86_perf_task_context *task_ctx)
>  
>  void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in)
>  {
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>  	struct x86_perf_task_context *task_ctx;
>  
> +	if (!cpuc->lbr_users)
> +		return;
> +
>  	/*
>  	 * If LBR callstack feature is enabled and the stack was saved when
>  	 * the task was scheduled out, restore the stack. Otherwise flush