linux-kernel - Re: [PATCH 0/9] perf: Adding better precise

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Message-ID: <20130510095345.GG3039@dyad.programming.kicks-ass.net>
Date:	Fri, 10 May 2013 11:53:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 0/9] perf: Adding better precise_ip field handling

On Fri, May 10, 2013 at 11:40:53AM +0200, Jiri Olsa wrote:
> nope, but I need a automated way to find out if PEBS
> is supported in system

Create an event, see what happens ;-) But I suppose you want to know if it
should have worked vs does it actually work? Yeah, I suppose what you did
is the right thing there.

I was just completely missing the rationale earlier.

> > > having maximum precise enabled with just single 'p' seemed
> > > like good idea
> > 
> > Doesn't seem like to me; that takes away the possibility to use less.
> 
> hm, we could have another modifier to get system precise value
> 'P' maybe.. and keep the 'p' logic

That might be a possibility indeed.

> > Also, you really don't need the max_precise for that either. At worst you'll
> > have a number of unsuccessful event creations.
> 
> so you mean just detect that by opening events with increasing
> precise and see how far we could get.. could be I guess, though
> the 'precise' sysfs attribute seems more fit to me

The other way around, start at ppp end at !p, then use the one that worked.
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