linux-kernel - Re: [RESEND PATCH V2 1/4] perf/x86/intel: fix event update for auto-reload

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Date:   Wed, 10 Jan 2018 11:22:49 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...el.com
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        eranian@...gle.com, ak@...ux.intel.com,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [RESEND PATCH V2 1/4] perf/x86/intel: fix event update for
 auto-reload

On Mon, Jan 08, 2018 at 07:15:13AM -0800, kan.liang@...el.com wrote:

SNIP

> There is nothing need to do in x86_perf_event_set_period(). Because it
> is fixed period. The period_left is already adjusted.
> 
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
>  arch/x86/events/intel/ds.c | 69 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 67 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index 3674a4b..cc1f373 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1251,17 +1251,82 @@ get_next_pebs_record_by_bit(void *base, void *top, int bit)
>  	return NULL;
>  }
>  
> +/*
> + * Specific intel_pmu_save_and_restart() for auto-reload.
> + */
> +static int intel_pmu_save_and_restart_reload(struct perf_event *event,
> +					     u64 reload_val,
> +					     int reload_times)
> +{
> +	struct hw_perf_event *hwc = &event->hw;
> +	int shift = 64 - x86_pmu.cntval_bits;
> +	u64 prev_raw_count, new_raw_count;
> +	u64 delta;
> +
> +	if ((reload_times == 0) || (reload_val == 0))
> +		return intel_pmu_save_and_restart(event);

why is this check needed? AFAICS __intel_pmu_pebs_event is
called only if reload_times != 0 and reload_val is always
non zero for sampling

jirka