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

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Date: Fri, 28 Jun 2024 20:55:50 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: x86@...nel.org, 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 Tue, Jun 25, 2024 at 9:04 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> 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.

Applied now, as 6.11 material.

Thanks!