linux-kernel - Re: [tip:perf/core] perf/x86: Use INST_RETIRED.PREC

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Message-ID: <20151207141242.GA6357@twins.programming.kicks-ass.net>
Date:	Mon, 7 Dec 2015 15:12:42 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>, vincent.weaver@...ne.edu,
	jolsa@...hat.com, torvalds@...ux-foundation.org,
	eranian@...gle.com, tglx@...utronix.de, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/x86: Use INST_RETIRED.PREC_DIST for cycles:
 ppp

On Mon, Dec 07, 2015 at 11:02:58AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Dec 07, 2015 at 07:48:41AM +0100, Ingo Molnar escreveu:
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > > On Sun, Dec 06, 2015 at 02:11:02PM +0100, Ingo Molnar wrote:
> > > > Also, I'm not convinced we need a new 'ppp' qualifier for any of this, why not 
> > > > just replace 'pp' with this event - 'pp' is meant to be our most precise 
> > > > event.
> 
> > > I requested this because the PREC_DIST events can only be scheduled on a single 
> > > counter, whereas the existing :pp events can be had on all 4.
> 
> > > This mean you can have 2 concurrent :pp users (without RR), but not :ppp.
> 
> > Ok. Will tooling do the right thing? I.e. will the first user of 'perf top' get 
> > :ppp automatically, while the second one falls back to :pp?
> 
> I guess so:
> 
> void perf_event_attr__set_max_precise_ip(struct perf_event_attr *attr)
> {
>         attr->precise_ip = 3;

Indeed so, I've since confirmed it does also works in practise.
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