Re: Getting started with perf; a couple of questions

[David Ahern <dsahern@gmail.com>]

On 5/31/13 2:35 PM, Andrew Davidoff wrote:
> On Fri, May 31, 2013 at 1:09 AM, Andrew Davidoff <davidoff@qedmf.net> wrote:
>> I will play with this more tomorrow but any further advice is
>> appreciated. I feel like I'm probably just missing a switch or
>> something that's not entirely obvious from the scant documentation I
>> have found.
>
> After struggling a bit more with this on the original host:
>
> Ubuntu 10.04.4 LTS
> kernel 2.6.32-47-server
> perf versions 3.9.4 and 3.8.13
>
> with no change in results, I gave it a shot on a CentOS 6 virtual
> machine on my Mac:
>
> CentOS release 6.4 (Final)
> kernel 3.9.4 AND kernel 2.6.32-358.2.1.el6.x86_64
> perf version 3.9.4
>
> And perf record is working as I'd expect it to. To be clear about the
> description above, under CentOS,  perf record 3.9.4 is recording
> samples whether I'm running kernel 3.9.4 or 2.6.32-358.2.1.el6.x86_64.

It's a VM and not running on KVM so there is no PMU which means the -e 
cycles is most likely falling back to -e cpu-clock. You should see this 
in a message with the -v flag on record. perf-script should dump out the 
events and show cpu-clock versus cycles.

Based on that I suggest trying -e cpu-clock on your original host. If 
that works then something is messed up with the pmu config on the host.

David
>
> So...Ubuntu thing? Or maybe just a 10.04 thing (yeah, I know it's old).
>
> Maybe this'll help someone.
>
> Thanks all.
> Andy
>