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

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Message-ID: <738e2dcc26926ce948bc7647cf17d83ed5d637b7.camel@intel.com>
Date: Wed, 3 Jul 2024 04:07:34 +0000
From: "Zhang, Rui" <rui.zhang@...el.com>
To: "peterz@...radead.org" <peterz@...radead.org>, "Dhananjay.Ugwekar@....com"
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Subject: Re: [PATCH v3 08/10] perf/x86/rapl: Modify the generic variable names
 to *_pkg*

On Tue, 2024-07-02 at 15:50 +0530, Dhananjay Ugwekar wrote:
> 
> > 
> > For Intel products, we have
> > 1. Casecadelake-AP which has multi-die per package and has per-die
> > RAPL
> > MSRs
> > 2. all other platforms which has single-die per package, so its
> > RAPL
> > MSRs can be considered as either package-scope or die-scope
> > This applies to Thermal MSRs as well.
> > 
> > so for these MSRs, we can treat them as
> > 1. always die-scope for all existing platforms
> > or
> > 2. package-scope with the exception of Casecadelake-ap
> > And current kernel code follows rule 1.
> > 
> > I propose we switch to rule 2 for these code because rule 1 can be
> > broke on future multi-die systems (This is already true for Thermal
> > MSRs).
> 
> 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 but it is just lucky that RAPL control is not exposed via the
MSRs so rule 1 is not actually broke for RAPL PMU (while it is indeed
broken for other drivers like thermal).

In short, if we stick with rule 1, the RAPL PMU still works. Switching
to rule 2 to be consistent with the other drivers is also a choice IMV.

thanks,
rui
> 
> If yes, then rule 1 above seems better.
> 
> Regards,
> Dhananjay
> 
> > 
> > In this sense, I think it is okay to call it pkg level rapl for
> > both
> > Intel and AMD.
> > 
> > thanks,
> > rui
> >