Re: perf tool/perf_event_open and uncore events

[Andi Kleen <andi@firstfloor.org>]

Manuel Selva <selva.manuel@gmail.com> writes:
>
> + It seems impossible to have per thread mode with this uncore
> event. I have to specify the -a or the -C option to the perf tool to
> get some results. Looking at the perf_event_open system call happening
> behind the scene, and calling it myself from code, I noticed that the
> call succeeded only when the pid parameter is -1 and the cpu one is
> different from -1. I guess that per thread counting is not available
> for uncore events because it's impossible for the hardware to measure
> only the uncore events generated by a given thread (because by
> definition uncore is shared by all the cores associated to it) Am I
> right ?

Yes uncore counting is per socket counting.
>
> + How the cpu parameter to perf_event_open should be interpreted for
> uncore events ? On my platform I have 12 cores (my two cpus are hexa
> core ones and hyper threading is disabled). Does providing a cpu value
> of 5 to the system call along with an uncore event means counting the
> events on the uncore associated to the core 5 ?

Yes, the socket associated with the CPU is used.

-Andi


-- 
ak@linux.intel.com -- Speaking for myself only