linux-kernel - Re: [PATCH v2 0/7] cpufreq: intel_pstate: Enable EAS on hybrid platforms without SMT

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Message-ID: <CAJZ5v0jLpKEgAodWx8G0k127vMUe-J1rGkCEreRP7a1dQXT2vA@mail.gmail.com>
Date: Tue, 13 May 2025 14:51:55 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>, 
	Peter Zijlstra <peterz@...radead.org>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Morten Rasmussen <morten.rasmussen@....com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, 
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, 
	Pierre Gondois <pierre.gondois@....com>, Christian Loehle <christian.loehle@....com>, 
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v2 0/7] cpufreq: intel_pstate: Enable EAS on hybrid
 platforms without SMT

On Tue, May 6, 2025 at 10:49 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> Hi Everyone,
>
> This is a new (and most likely final) version of
>
> https://lore.kernel.org/linux-pm/3344336.aeNJFYEL58@rjwysocki.net/
>
> The most significant difference between it and the above is that schedutil is
> now required for EAS to be enabled, like on the other platforms using EAS,
> which means that intel_pstate needs to operate in the passive mode in order
> to use it (the most straightforward way to switch it over to the passive mode
> is to write "passive" to /sys/devices/system/cpu/intel_pstate/status).
>
> Accordingly, the changes that were needed for EAS to work without schedutil are
> not needed any more, so there is one patch less in the series because of that
> and patch [5/7] is simpler than its previous version because some changes made
> by it are not necessary any more.
>
> Another patch that has been dropped is
>
> https://lore.kernel.org/linux-pm/1964444.taCxCBeP46@rjwysocki.net/
>
> because it didn't take CPU online into account properly and it is not essential
> for the current hardware anyway.
>
> There is a new patch, [7/7], which adds CAS/EAS/hybrid support description to
> the intel_pstate admin-guide documentation.
>
> The following paragraph from the original cover letter still applies:
>
> "The underlying observation is that on the platforms targeted by these changes,
> Lunar Lake at the time of this writing, the "small" CPUs (E-cores), when run at
> the same performance level, are always more energy-efficient than the "big" or
> "performance" CPUs (P-cores).  This means that, regardless of the scale-
> invariant utilization of a task, as long as there is enough spare capacity on
> E-cores, the relative cost of running it there is always lower."
>
> The first 2 patches depend on the current cpufreq material queued up for 6.16
> in linux-pm.git/linux-next (and in linux-next proper) and are not really
> depended on by the rest of the series, but I've decided to include them into
> this series because they have been slightly updated since the previous version,
> mostly to take review feedback into account (I'm going to queue them up for
> 6.16 shortly because they don't appear to be objectionable).
>
> The next 2 patches (Energy Model code changes) were reviewed previously, but
> they are only needed because of patch [5/7].
>
> Patch [5/7] has not changed much except that some changes made by the previous
> version have been dropped from it.  Also its changelog has been updated.  It
> causes perf domains to be registered per CPU and in addition to the primary cost
> component, which is related to the CPU type, there is a small component
> proportional to performance whose role is to help balance the load between CPUs
> of the same type.
>
> The expected effect is still that the CPUs of the "low-cost" type will be
> preferred so long as there is enough spare capacity on any of them.
>
> Patch [6/7] has been updated to walk all of the cache leaves and look for
> the ones with level equal to 3 because the check used in the previous version
> does not always work.
>
> The documentation patch, [7/7], is new.
>
> Please refer to the individual patch changelogs for details.

This series along with the fix at

https://lore.kernel.org/linux-pm/2806514.mvXUDI8C0e@rjwysocki.net/

is now present in the experimental/intel_pstate/eas-final brangh in
linux-pm.git:

https://web.git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/log/?h=experimental/intel_pstate/eas-final

and it has been added to the bleeding-edge branch for 0-day build testing.

Thanks!