Re: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read from any CPU

[Mark Rutland]

On Mon, Feb 26, 2018 at 05:53:57PM -0800, skannan@xxxxxxxxxxxxxx wrote:
> On 2018-02-24 00:41, Peter Zijlstra wrote:
> > On Fri, Feb 23, 2018 at 04:19:38PM -0800, Saravana Kannan wrote:
> > > Some PMUs events can be read from any CPU. So allow the PMU to mark
> > > events as such. For these events, we don't need to reject reads or
> > > make smp calls to the event's CPU and cause unnecessary wake ups.
> > > 
> > > Good examples of such events would be events from caches shared across
> > > all CPUs.
> > 
> > So why would the existing ACTIVE_PKG not work for you? Because clearly
> > your example does not cross a package.
> 
> Because based on testing it on hardware, it looks like the two clusters in
> an ARM DynamIQ design are not considered part of the same "package". 

I don't think we should consider the topology masks at all for system
PMU affinity. Due to the number of ways these can be integrated, and the
lack of a standard(ish) topology across arm platforms.

IIUC, there's ongoing work to try to clean that up, but that won't give
us anything meaningful for PMU affinity.

If we need a mask, that should be something the FW description of the
PMU provides, and the PMU driver provides to the core code.

Thanks,
Mark.