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

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Date: Tue, 2 Jul 2024 15:50:30 +0530
From: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
To: "Zhang, Rui" <rui.zhang@...el.com>,
 "peterz@...radead.org" <peterz@...radead.org>
Cc: "gautham.shenoy@....com" <gautham.shenoy@....com>,
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 <namhyung@...nel.org>
Subject: Re: [PATCH v3 08/10] perf/x86/rapl: Modify the generic variable names
 to *_pkg*

Hello Rui,

On 7/2/2024 7:55 AM, Zhang, Rui wrote:
> On Mon, 2024-07-01 at 15:08 +0200, Peter Zijlstra wrote:
>> On Mon, Jun 24, 2024 at 05:59:05AM +0000, Dhananjay Ugwekar wrote:
>>> Prep for addition of power_per_core PMU to handle core scope energy
>>> consumption for AMD CPUs.
>>>
>>> Replace the generic names with *_pkg*, to differentiate between the
>>> scopes of the two different PMUs and their variables.
>>
>> But then remember patch 2 and recall that intel seems to have
>> everything
>> at die level, not pkg.
>>
>> Does this proposed naming make sense? How?
> 
> 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?

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
>