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

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Date:   Thu, 11 Jan 2018 11:54:46 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     kan.liang@...el.com, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        eranian@...gle.com, ak@...ux.intel.com
Subject: Re: [RESEND PATCH V2 1/4] perf/x86/intel: fix event update for
 auto-reload

On Wed, Jan 10, 2018 at 09:31:01AM -0500, Liang, Kan wrote:
> 
> 
> On 1/10/2018 5:22 AM, Jiri Olsa wrote:
> > 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
> > 
> 
> Here is a sanity check for reload_times and reload_val.
> Right, usually they are non zero.
> I think it should not bring any issues. Right?
> If so, I think we may still keep it?

sure, no big deal.. I just don't see the reason ;-)

jirka