linux-kernel - Re: [PATCH v3 4/4] perf,x86: add RAPL hrtimer support

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Message-ID: <20131025174448.GD7024@krava.brq.redhat.com>
Date:	Fri, 25 Oct 2013 19:44:48 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	ak@...ux.intel.com, acme@...hat.com, zheng.z.yan@...el.com,
	bp@...en8.de
Subject: Re: [PATCH v3 4/4] perf,x86: add RAPL hrtimer support

On Wed, Oct 23, 2013 at 02:58:05PM +0200, Stephane Eranian wrote:
> The RAPL PMU counters do not interrupt on overflow.
> Therefore, the kernel needs to poll the counters
> to avoid missing an overflow. This patch adds
> the hrtimer code to do this.
> 
> The timer internval is calculated at boot time
> based on the power unit used by the HW.
> 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel_rapl.c |   75 +++++++++++++++++++++++++--
>  1 file changed, 70 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_rapl.c b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
> index 3d71d39..ed0566a 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_rapl.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
> @@ -92,11 +92,13 @@ static struct kobj_attribute format_attr_##_var =		\
>  
>  struct rapl_pmu {
>  	spinlock_t	lock;
> -	atomic_t	refcnt;
>  	int		hw_unit;  /* 1/2^hw_unit Joule */
> -	int		phys_id;
> -	int		n_active; /* number of active events */
> +	struct hrtimer	hrtimer;
>  	struct list_head active_list;
> +	ktime_t		timer_interval; /* in ktime_t unit */
> +	int		n_active; /* number of active events */
> +	int		phys_id;
> +	atomic_t	refcnt;
>  };
>  
>  static struct pmu rapl_pmu_class;
> @@ -161,6 +163,47 @@ static u64 rapl_event_update(struct perf_event *event)
>  	return new_raw_count;
>  }
>  
> +static void rapl_start_hrtimer(struct rapl_pmu *pmu)
> +{
> +	__hrtimer_start_range_ns(&pmu->hrtimer,
> +			pmu->timer_interval, 0,
> +			HRTIMER_MODE_REL_PINNED, 0);
> +}
> +
> +static void rapl_stop_hrtimer(struct rapl_pmu *pmu)
> +{
> +	hrtimer_cancel(&pmu->hrtimer);
> +}
> +
> +static enum hrtimer_restart rapl_hrtimer_handle(struct hrtimer *hrtimer)
> +{
> +	struct rapl_pmu *pmu = container_of(hrtimer, struct rapl_pmu, hrtimer);
> +	struct perf_event *event;
> +	unsigned long flags;
> +
> +	if (!pmu->n_active)
> +		return HRTIMER_NORESTART;
> +
> +	spin_lock_irqsave(&pmu->lock, flags);
> +
> +	list_for_each_entry(event, &pmu->active_list, active_entry) {
> +		rapl_event_update(event);
> +	}

hi,
I dont fully understand the reason for the timer,
I'm probably missing something..

- the timer calls rapl_event_update for all defined events
- but rapl_pmu_event_read calls rapl_event_update any time the
  event is read (sys_read)

The rapl_event_update only read msr and updates
event->count|hw,prev_count.

What's the timer purpose then?

thanks for info,
jirka
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