[PATCH 0/3] drm/panfrost: Expose HW counters to userspace

[Boris Brezillon]

On Fri, 5 Apr 2019 09:33:55 -0700
Alyssa Rosenzweig <alyssa at rosenzweig.io> wrote:

> > Since one of the primary use cases is to draw pretty graphs of the
> > system load [1], this "per-job" information isn't all that relevant (and
> > minimal performance overhead is important). And if you want to monitor
> > just one application it is usually easiest to ensure that it is the only
> > thing running.  
> 
> Ah-ha, gotch. I don't know why I didn't put 2 and 2 together, but that
> definitely makes sense, yeah :) Boris, thoughts?

Nothing to add, except, I had the gut feeling I was doing the wrong
choice here, hence the mention to this design decision in my cover
letter :-).
I'll rework the implementation to have perfmons apply globally (instead
of being attached to jobs) and get rid of the perfcnt fence.

Note that we could support both per-job and global perfmons and avoid
the perf penalty when only global perfmons are used, but I don't think
it's worth the extra complexity (not to mention that it makes things
even more confusing for userspace users).