Re: [RFC 0/4] perf tool: Adding ratios support

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Jan 16, 2013 at 01:13:18PM +0000, Will Deacon wrote:
> On Tue, Jan 15, 2013 at 01:39:50PM +0000, Jiri Olsa wrote:
> > hi,
> 
> Hi Jiri,
> 
> > adding support to predefine event ratios formulas so they could
> > be used easily in perf.
> > 
> > The formulas are handed in the config file with following format:
> > 
> >   set {
> >         events = {cycles,instructions,branch-instructions}:u
> > 
> >         cpi {
> >                 formula = cycles / instructions
> >                 desc = cycles per instruction
> >         }
> > 
> > 	branch-rate {
> >                 formula = branch-instructions / instructions
> >                 desc = branch rate
> >         }
> >   }
> > 
> >   The 'set' defines set of counter that share same events.
> >   Each 'set' defines:
> >     events   - event string that would go into stat/record -e option
> >     counters - any number of counters based on above events
> > 
> >   Each counter (cpi/branch-rate) defines
> >     formula - formula with that produce the counter number
> >               event names and numbers could be used
> >     desc    - text description of the counter
> > 
> > The formula can currently contain any event from the set::events
> > plus any number (int). There'll be support in future for outside
> > values runtime and other if needed.
> 
> Just to say that I *really* like this idea! If we extended it to include
> other operators then it would help us on ARM, where we often have events
> like 'cache accesses' and 'cache misses' but not 'cache hits'.

great, thanks for sharing this

The current operators set is just basic one to show the idea,
it can/will be expanded.

> 
> > My current thinking is to have generic formulas file(s) for architectural
> > events and add arch-specific ones once when we have the support for
> > non-architectural events (already sent RFC, v2 is on its way..).
> 
> Would the architectural formula files also be in userspace, or is there any
> merit to including useful PMU-specific formulae in sysfs, along with the
> other PMU files?

hum, isn't this too specific for sysfs files?

I think that's going to be the perf tool specific info.. so it's going
to be placed in its configuration files.


jirka