linux-kernel - Re: [RFC] perf/x86/intel: Account interrupts for PEBS errors

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Date:   Wed, 14 Dec 2016 19:16:36 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andi Kleen <andi@...stfloor.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Vince Weaver <vince@...ter.net>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC] perf/x86/intel: Account interrupts for PEBS errors

On Wed, Dec 14, 2016 at 07:07:30PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 14, 2016 at 05:50:36PM +0100, Jiri Olsa wrote:
> > 
> > I also fail to reproduce on other than snb_x (model 45) server
> 
> reproduces on my ivb-ep as well model 62.
> 
> > thoughts?
> 
> cute find :-)
> 
> > +++ b/arch/x86/events/intel/ds.c
> > @@ -1389,9 +1389,13 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs)
> >  			continue;
> >  
> >  		/* log dropped samples number */
> > -		if (error[bit])
> > +		if (error[bit]) {
> >  			perf_log_lost_samples(event, error[bit]);
> >  
> > +			if (perf_event_account_interrupt(event, 1))
> 
> Seems a bit daft to expose the .throttle argument, since that would be
> the only point of calling this.

there's also the other caller from __perf_event_overflow

> > +static int __perf_event_overflow(struct perf_event *event,
> > +				   int throttle, struct perf_sample_data *data,
> > +				   struct pt_regs *regs)
> > +{
> > +	int events = atomic_read(&event->event_limit);
> > +	struct hw_perf_event *hwc = &event->hw;
> > +	int ret = 0;
> > +
> > +	/*
> > +	 * Non-sampling counters might still use the PMI to fold short
> > +	 * hardware counters, ignore those.
> > +	 */
> > +	if (unlikely(!is_sampling_event(event)))
> > +		return 0;
> > +
> > +	ret = perf_event_account_interrupt(event, throttle);
> > +
> >  	if (event->attr.freq) {
> >  		u64 now = perf_clock();
> >  		s64 delta = now - hwc->freq_time_stamp;
> 
> Arguably, everything in __perf_event_overflow() except for calling of
> ->overflow_handler() should be done I think.

well, I was wondering about that period adjustment bit

but I wasn't sure about those pending_kill/pending_wakeup bits,
they make sense to me only if we have some data to deliver


jirka