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Subject: Re: [RFC][PATCH v0.1 3/6] PM: EM: Add special case to
 em_dev_register_perf_domain()
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
 Linux PM <linux-pm@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Lukasz Luba <lukasz.luba@arm.com>,
 Peter Zijlstra <peterz@infradead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
 Len Brown <len.brown@intel.com>, Morten Rasmussen
 <morten.rasmussen@arm.com>, Vincent Guittot <vincent.guittot@linaro.org>,
 Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
References: <3607404.iIbC2pHGDl@rjwysocki.net>
 <2017201.usQuhbGJ8B@rjwysocki.net>
From: Dietmar Eggemann <dietmar.eggemann@arm.com>
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On 08/11/2024 17:38, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Allow em_dev_register_perf_domain() to register a cost-only stub
> perf domain with one-element states table if the .active_power()
> callback is not provided.
> 
> Subsequently, this will be used by the intel_pstate driver to register
> stub perf domains for CPUs on hybrid systems.

Looks like a 'stub' PD only distinguish itself from a normal PD by not
checking that all CPU in that PD have the same CPU capacity value?

I assume you do this since the Performance Cores (CPUs) can have
different CPU capacity values due to slightly different 'itmt prio' values?

So strictly speaking such a Intel hybrid machine would be tri-gear
system to fit the definition of a PD.

I thought initially by reading the word 'stub' that you only setup a
part of the default EM infrastructure.

[...]