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

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Date:	Wed, 20 Jul 2016 17:36:46 +0300
From:	Nikolay Borisov <kernel@...p.com>
To:	Jiri Olsa <jolsa@...hat.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 07/20/2016 05:34 PM, 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..

FYI running perf top -e instructions:p also produces no data on that
particular CPU.

> 
> I'll check why perf top forcing the precise for cycles
> I thought we had that automated already
> 
> jirka
>