Re: [RFC PATCH 0/3] perf: show package power consumption in perf

[Ingo Molnar <mingo@elte.hu>]

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, 2010-08-20 at 09:44 +0800, Zhang Rui wrote:
> > On Thu, 2010-08-19 at 17:02 +0800, Peter Zijlstra wrote:
> 
> > > its some obscure perf feature:
> > > 
> > >  leader = sys_perf_event_open(&hrtimer_attr, pid, cpu, 0, 0);
> > >  sibling = sys_perf_event_open(&rapl_attr, pid, cpu, leader, 0);
> > > 
> > > will create an even group (which means that both events require to be
> > > co-scheduled). If you then provided:
> > > 
> > > hrtimer_attr.read_format |= PERF_FORMAT_GROUP;
> > > hrtimer_attr.sample_type |= PERF_SAMPLE_READ;
> > > 
> > hrtimer_attr is only shared in an event group, and rapl needs its owen
> > event group, right?
> 
> Uhm, no. The idea is to group the hrtimer and rapl event in order to
> obtain rapl 'samples'.
> 
> That is, you get hrtimer samples which include the rapl count. For this
> we use the grouping construct where group siblings are always
> co-scheduled and can report on each others count.
> 
> > so what do you think the rapl counter should look like in userspace?
> > showing it in perf-stat looks nice, right? :)
> 
> Right, so the userspace interface would be using Lin's sysfs bits, which I 
> still need to read up on. But the general idea is that each PMU gets a sysfs 
> representation somewhere in the system topology reflecting its actual site 
> (RAPL would be CPU local), this sysfs representation would then also allow 
> you to discover all events it provides.
> 
> perf list will then use sysfs to discover all available events, and you can 
> still use perf stat -e $foo to select it, where foo is some to be determined 
> string that identifies the thing, maybe something like: rapl:watts or 
> somesuch (with rapl identifying the pmu and watts the actual event for that 
> pmu).

Btw., some 'perf list' thoughts. We could do a:

   perf list --help rapl:watts

Which gives the user some idea what an event does. Also, short descriptive 
line in perf list output would be nice:

$ perf list

List of pre-defined events (to be used in -e):

  cpu-cycles OR cycles                       [Hardware event]   # CPU cycles
  instructions                               [Hardware event]   # instructions executed

  ...

  rapl:watts                                 [Tracepoint]       # watts usage

or something like that. Perhaps even a TUI for perf list, to browse between 
event types? (in that case it would probably be useful to make them collapse 
along natural grouping)

We want users/developers to discover new events, see and understand their 
purpose and combine them in not-seen-before ways.

Thanks,

	Ingo