[PATCH 5/5] arm/perfevents: implement perf event support for ARMv6

[Jamie Iles]

On Wed, Dec 16, 2009 at 11:04:09AM -0000, Will Deacon wrote:
> *Jamie Iles wrote:
> 
> > > That's exactly what I do for single core ARMv6. However, in the list of events
> > > for mpcore I can't see any that wouldn't count. There's plenty of reserved
> > > identifiers though so hopefully one of those will do the job. Also, ARM
> > > counters can't be set to exclude any modes.
> >
> > Thinking about this a bit more, although we can't disable the counters, we can
> > disable their interrupt reporting. So, when the generic perf events layer
> > calls pmu->disable(event), we do the update of the event then turn off the
> > IRQ. When we come to unthrottling, the counter will have carried on counting,
> > but if we set the period again, the counter gets set with the correct restart
> > value and then reenabled.
> 
> This was my first thought, but I was concerned about how it would play out
> with the armpmu_read function. Now that I see we don't read disabled counters,
> I can't see any reason not to simply disable the interrupt and stash the count
> value.
We shouldn't even need to stash the value. When the higher layer disables the
event we sample it to record the value so the stashing happens already.

> > I think this should work for mpcore and is also required for the cycle counter
> > on all v6 cores. I've given this a go using an artificially low period on a
> > cycle counter and it does appear to do the job.
> 
> If we do this for mpcore, is it worth doing the same thing for the other v6 cores
> too [and removing the ETM `hack']?
We do need to do this on UP v6 for the cycle counter as that keeps on running,
but imho the ETM hack is worth keeping as it really does stop the counter. It
doesn't hurt and we're guaranteed not to lose any events.

If I make the change to the unthrottling and the Kconfig and tab changes, and
add the mpcore events does anyone have an objection to making a final version
of this patch series and merging it?

Jamie