Re: [RFC] perf_events: support for uncore a.k.a. nest units

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2010-01-28 at 10:00 -0800, Corey Ashford wrote:
> 
> I don't quite get what you're saying here.  Perhaps you are thinking 
> that all uncore units are associated with a particular cpu node, or a 
> set of cpu nodes?  And that there's only one uncore unit per cpu (or set 
> of cpus) that needs to be addressed, i.e. no ambiguity?

Well, I was initially thinking of the intel uncore thing which is memory
controller, so node, level.

But all system topology bound pmus can be done that way.

> That is not going to be the case for all systems.  We can have uncore 
> units that are associated with the entire system,

Right, but that's simple too.

> for example PMUs in an I/O device.  

> And we can have multiple uncore units of a particular 
> type, for example multiple vector coprocessors, each with its own PMU, 
> and are associated with a single cpu or a set of cpus.
> 
> perf_events needs an addressing scheme that covers these cases. 

You could possible add a u64 pmu_id field to perf_event_attr and use
that together with things like:

  PERF_TYPE_PCI, attr.pmu_id = domain:bus:device:function encoding
  PERF_TYPE_SPU, attr.pmu_id = spu-id

But before we go there the perf core needs to be extended to deal with
multiple hardware pmus, something which isn't too hard but we need to be
careful not to bloat the normal code paths for these somewhat esoteric
use cases.