Re: perf record and intel_cqm/llc_occupancy

[Andi Kleen <andi@firstfloor.org>]

On Fri, Jun 24, 2016 at 12:27:27PM +0000, Omar Awile wrote:
> Hi Andi,
> 
> Thanks, I see your point. I’ve seen tried perf stat for these events, which is quite nice. However, we would like to be able to correlate the cache occupancy with the current call stack. I don’t see how this could be done with perf stat. Is there a way to do this?

perf stat cannot collect call graphs.

> 
> Alternatively, since perf record already keeps track of the call stack, is it feasible to extend it to allow recording cache occupancy, or is this inherently impossible?

perf can collect counts while sampling another event (called leader
sampling using :S). Unfortunately this does not work with events from
different PMUs, which would be needed here. Kan looked into this
some time ago, but there were too many problems with it.

> 
> Finally, if none of the two alternatives work, do you have an idea how else this could be achieved?

For now the only way would be to sample and perf stat record in parallel
and then merge the data based on the time stamps. It likely will not
be very accurate.

-Andi