On Fri, Jul 24, 2020 at 04:59:34PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 24, 2020 at 07:46:32AM -0700, Andi Kleen wrote:
> > > Something that seems to 'work' is:
> > > '{cycles,cpu/instructions,period=50000/}', so maybe you can make the
> > > group modifier :S use any sampling event if there is one, and otherwise
> > > designate the leader.
> > >
> > > Then you can write things like:
> > >
> > > '{slots, metric1, metric2, cpu/cycles,freq=50000/}:S'
> > >
> > > and then since cycles is specified as a sampling event, it will use
> > > that.
> >
> > Okay possible, but it makes things more complicated
> > for the user to understand and requires special documentation.
> > Hopefully it's worth it the internal simplification.
>
> You already require special documentation for this metrics stuff. We
> already need to state that SLOTS cannot be a sampling event, so you
> already need to pay attention to this anyway.
>
> A shortcut could be a :s event modifier, then you can write:
>
> '{slots, metric1, metric2, cycles:s}:S'
>
> and have the tool select the :s tagged one.
Having slots as leader also would allow doing something like
FORMAT_METRIC, where we return sibling/leader in some fashion.
That also makes sense for instructions, because, IIRC,
instructions/slots is the better IPC.
And we should probably consider FORMAT_RESET.
