Re: [PATCH 01/32] perf: Allow a PMU to have a parent

[Mark Rutland]

On Thu, Apr 06, 2023 at 09:49:38PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 06, 2023 at 05:44:45PM +0100, Jonathan Cameron wrote:
> > On Thu, 6 Apr 2023 14:40:40 +0200
> > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > 
> > > On Thu, Apr 06, 2023 at 11:16:07AM +0100, Jonathan Cameron wrote:
> > > 
> > > > In the long run I agree it would be good.  Short term there are more instances of
> > > > struct pmu that don't have parents than those that do (even after this series).
> > > > We need to figure out what to do about those before adding checks on it being
> > > > set.  
> > > 
> > > Right, I don't think you've touched *any* of the x86 PMUs for example,
> > > and getting everybody that boots an x86 kernel a warning isn't going to
> > > go over well :-)
> > > 
> > 
> > It was tempting :) "Warning: Parentless PMU: try a different architecture."
> 
> Haha!
> 
> > I'd love some inputs on what the x86 PMU devices parents should be?
> > CPU counters in general tend to just spin out of deep in the architecture code.
> 
> For the 'simple' ones I suppose we can use the CPU device.

Uh, *which* CPU device? Do we have a container device for all CPUs?

> > My overall favorite is an l2 cache related PMU that is spun up in
> > arch/arm/kernel/irq.c init_IRQ()

That's an artifact of the L2 cache controller driver getting initialized there;
ideally we'd have a device for the L2 cache itself (which presumably should
hang off an aggregate CPU device).

> Yeah, we're going to have a ton of them as well. Some of them are PCI
> devices and have a clear parent, others, not so much :/

In a number of places the only thing we have is the PMU driver, and we don't
have a driver (or device) for the HW block it's a part of. Largely that's
interconnect PMUs; we could create container devices there.

Mark.