linux-kernel - Re: [PATCH V3 0/5] bugs fix for large PEBS mmap read and rdpmc read

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Message-ID: <20180130185212.GA16806@krava>
Date:   Tue, 30 Jan 2018 19:52:12 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH V3 0/5] bugs fix for large PEBS mmap read and rdpmc read

On Tue, Jan 30, 2018 at 11:48:18AM -0500, Liang, Kan wrote:

SNIP

> > > 
> > > The events in fixed mode could enable large PEBS. Events in freq mode should
> > > not enable large PEBS.
> > > I think that could be a problem if some events try to enable large PEBS,
> > > while others not.
> > > 
> > You only enable large PEBS if 100% of the events use fixed periods,
> > either via -c period
> > or because they all use individual period=p. The --no-period could
> > also be used to remove
> > the period for measurements where the period is not needed.
> 
> 
> Oh, right, the kernel has already guaranteed that.
> 	if (cpuc->n_pebs == cpuc->n_large_pebs) {
> 		threshold = ds->pebs_absolute_maximum -
> 			x86_pmu.max_pebs_events * x86_pmu.pebs_record_size;
> 	} else {
> 
> Sorry for the noise.
> 
> jirka's patch looks good to me.

cool, I'll post it later this week

thanks,
jirka