linux-kernel - Re: [PATCH v3 08/10] perf/x86/rapl: Modify the generic variable names to *

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Message-ID: <20240705092416.GB11386@noisy.programming.kicks-ass.net>
Date: Fri, 5 Jul 2024 11:24:16 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Zhang, Rui" <rui.zhang@...el.com>
Cc: "Dhananjay.Ugwekar@....com" <Dhananjay.Ugwekar@....com>,
	"gautham.shenoy@....com" <gautham.shenoy@....com>,
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Subject: Re: [PATCH v3 08/10] perf/x86/rapl: Modify the generic variable
 names to *_pkg*

On Fri, Jul 05, 2024 at 02:18:30AM +0000, Zhang, Rui wrote:

> > > > I have a doubt about this, won't the future Intel multi-die
> > > > systems 
> > > > have die-scope for the RAPL PMU like Casecadelake-AP?
> > > 
> > > For future multi-die systems that I know, the RAPL is still package
> > > scope 
> > 
> > I think in that case we can go with rule 2, it would be future proof
> > for Intel systems. If you agree, I can make the change in next
> > version.
> > 
> > Something like below?,
> > 
> > -#define rapl_pmu_is_pkg_scope()                         \
> > -        (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || 
> > \                                                                    
> >                                                                      
> >                          
> > -        boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
> > 
> > +#define rapl_pmu_is_die_scope()                        \
> > +       (boot_cpu_data.x86_model_id == CASCADELAKE)
> > 
> sounds good to me. Just a reminder that using boot_cpu_data.vfm is a
> better choice here.
> 
> And it would be great to get Peter' view on this.

Peter is confused :-) So you're saying that:

 - old Intel is pkg wide (it has no DIE enumeration)
 - Cascadelake (part of the skylake refresh) is per-DIE
 - modern Intel is pkg wide (they have no DIE enumeration)
 - future Intel will be pkg wide

And this works because for everything that does not enumerate a specific
DIE topology, it ends up begin the same as the PKG topology.

But what about future products that have DIE but are not CASCADE (what
about COOPERLAKE) ?

If this really is a one off for CASCADE, then yes, I think we should be
doing what Dhananjay suggests, and then the PKG naming is fine.