linux-kernel - Re: [PATCH v2 0/2] Update highest frequency of a CPU after boot

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Message-ID: <CAJZ5v0iE_-eMi1JvWfDJM5-Z810WUdQPUoq9Qn8q62F5daXoSg@mail.gmail.com>
Date: Tue, 25 Jun 2024 21:04:13 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, x86@...nel.org
Cc: rafael@...nel.org, viresh.kumar@...aro.org, tglx@...utronix.de, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Update highest frequency of a CPU after boot

On Mon, Jun 24, 2024 at 6:11 PM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> Intel Xeon servers, which are capable of dynamic highest performance
> change, are unable to achieve the highest frequency when the performance
> profile is changed.
>
> The highest frequency at which a CPU can operate is not fixed and can
> vary after the system boots. These changes can be initiated by switching
> to different performance profiles using the Intel Speed Select Technology
> interface. Additionally, adjustments can be made remotely through a BMC
> (Baseboard Management Controller) interface. Administrators can select
> various performance profiles to align with specific performance
> requirements, as these choices will directly influence the total power
> consumption and cooling requirements.
>
> Whenever an administrator switches to a different performance profile that
> alters the highest frequency, the hardware sends an interrupt and update
> the new highest frequency at which the system can operate. This interrupt
> can be enabled via the MSR_HWP_INTERRUPT register, and only if support is
> indicated by the CPUID[6].EAX[15] = 1.
>
> To enable changes to the highest frequency, add a CPU features flag and
> enable the HWP (Hardware P-states) highest performance change interrupt
> when it is supported by the CPU.
>
> v2:
> - Prevent display in /proc/cpuinfo flags
> - Use cpu_feature_enabled() instead of boot_cpu_has()
>
> Srinivas Pandruvada (2):
>   x86/cpufeatures: Add HWP highest perf change feature flag
>   cpufreq: intel_pstate: Support highest performance change interrupt
>
>  arch/x86/include/asm/cpufeatures.h |  1 +
>  drivers/cpufreq/intel_pstate.c     | 23 +++++++++++++++++++----
>  2 files changed, 20 insertions(+), 4 deletions(-)
>
> --

Please let me know if there are objections against this from the x86 angle.

If not, I'll pick it up.

Thanks!