linux-kernel - Re: Strange behavior of perf top with PEBS

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Date:	Thu, 4 Aug 2016 17:29:26 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Nikolay Borisov <kernel@...p.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	andi@...stfloor.org
Subject: Re: Strange behavior of perf top with PEBS

On Tue, Jul 26, 2016 at 02:30:46PM +0300, Nikolay Borisov wrote:
> 
> 
> On 07/20/2016 05:38 PM, Jiri Olsa wrote:
> > On Wed, Jul 20, 2016 at 04:34:17PM +0200, Jiri Olsa wrote:
> >> On Wed, Jul 20, 2016 at 04:28:34PM +0300, Nikolay Borisov wrote:
> >>> Hello,
> >>>
> >>> Running perf version 4.4.14.g0cb188d (no modification to the PMU/perf
> >>> code) I observed that "perf top" counts no cycles and produces no
> >>> output. After a bit of head scratching and testing I figured that
> >>> running "perf top -e cycles" actually works whereas the default option
> >>> is equivalent to running "perf top -e cycles:p". So the latter version
> >>> seems to not work on my machine.
> >>
> >> hum, I think Core2 has PEBs valid only for instructions not cycles..
> >>
> >> I'll check why perf top forcing the precise for cycles
> >> I thought we had that automated already
> > 
> > oops, too soon ;) we have:
> > 
> > perf/x86/intel: Fix Core2,Atom,NHM,WSM cycles:pp events
> > commit 517e6341fa123ec3a2f9ea78ad547be910529881
> > Author: Peter Zijlstra <peterz@...radead.org>
> > Date:   Sat Apr 11 12:16:22 2015 +0200
> > 
> > 
> > so i guess it should work.. checking ;-)
> 
> Any update on that?

sorry for late response..

I checked on f22 kernel and it's missing the core2 PEBs fix:
  1424a09a9e18 perf/x86: fix PEBS issues on Intel Atom/Core2

which was introduced in 4.5.. you should upgrade or include
this patch

jirka