Re: Strange behavior of perf top with PEBS

From: Nikolay Borisov
Date: Wed Jul 20 2016 - 10:37:16 EST

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