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

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Date:	Mon, 7 Dec 2015 11:02:58 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.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

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;
<SNIP>

- Arnaldo
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