[RFC] Extending ARM perf-events for multiple PMUs

[peterz@infradead.org (Peter Zijlstra)]

On Mon, 2011-04-11 at 12:29 +0100, Will Deacon wrote:
> > If you've got system wide things like GPUs, where every cpu maps to the
> > same device, simply use the first online cpu and create a pmu instance
> > per device.
> 
> Would this result in userspace attributing all of the data to a
> particular CPU? We could consider allowing events where the cpu is -1
> and the task pid is -1 as well. Non system-wide PMUs could reject these
> and demand multiple events instead. 

Not at such, but you need a cpu to receive interrupts on and program the
hardware from etc. Currently most core code assumes things are either
restrained to a single cpu or serialized by virtue of a task never
running on more than 1 cpu at a time.

I'm not quite sure how hard these assumptions are, and we might be able
to get away with making it a little less strict, but that's something
you'd have to play with.