linux-kernel - RE: [PATCH v6] x86: intel_epb: Add earlyparam option to keep bias at performance

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Message-ID: <12f10bbcba78463fa274e17fad305894@amazon.co.uk>
Date: Thu, 4 Jan 2024 09:22:35 +0000
From: "Durrant, Paul" <pdurrant@...zon.co.uk>
To: "Allister, Jack" <jalliste@...zon.co.uk>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "Allister, Jack" <jalliste@...zon.co.uk>, "Rafael J . Wysocki"
	<rafael@...nel.org>, "Wang, Jue" <juew@...zon.com>, Usama Arif
	<usama.arif@...edance.com>, Jonathan Corbet <corbet@....net>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "x86@...nel.org"
	<x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, "Paul E. McKenney"
	<paulmck@...nel.org>, Randy Dunlap <rdunlap@...radead.org>, Tejun Heo
	<tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Yan-Jie Wang
	<yanjiewtw@...il.com>, Hans de Goede <hdegoede@...hat.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: RE: [PATCH v6] x86: intel_epb: Add earlyparam option to keep bias at
 performance

> -----Original Message-----
> From: Jack Allister <jalliste@...zon.com>
> Sent: 04 January 2024 09:06
> Cc: Allister, Jack <jalliste@...zon.co.uk>; Rafael J . Wysocki
> <rafael@...nel.org>; Durrant, Paul <pdurrant@...zon.co.uk>; Wang, Jue
> <juew@...zon.com>; Usama Arif <usama.arif@...edance.com>; Jonathan Corbet
> <corbet@....net>; Thomas Gleixner <tglx@...utronix.de>; Ingo Molnar
> <mingo@...hat.com>; Borislav Petkov <bp@...en8.de>; Dave Hansen
> <dave.hansen@...ux.intel.com>; x86@...nel.org; H. Peter Anvin
> <hpa@...or.com>; Paul E. McKenney <paulmck@...nel.org>; Randy Dunlap
> <rdunlap@...radead.org>; Tejun Heo <tj@...nel.org>; Peter Zijlstra
> <peterz@...radead.org>; Yan-Jie Wang <yanjiewtw@...il.com>; Hans de Goede
> <hdegoede@...hat.com>; linux-doc@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: [PATCH v6] x86: intel_epb: Add earlyparam option to keep bias at
> performance
> 
> Buggy BIOSes may not set a sane boot-time Energy Performance Bias (EPB).
> A result of this may be overheating or excess power usage. The kernel
> overrides any boot-time EPB "performance" bias to "normal" to avoid this.
> 
> When used in data centers it is preferable keep the EPB at "performance"
> when performing a live-update of the host kernel via a kexec to the new
> kernel. This is due to boot-time being critical when performing the kexec
> as running guest VMs will perceieve this as latency or downtime.
> 
> On Intel Xeon Ice Lake platforms it has been observed that a combination
> of
> EPB being set to "normal" alongside HWP (Intel Hardware P-states) being
> enabled/configured during or close to the kexec causes an increases the
> live-update/kexec downtime by 7 times compared to when the EPB is set to
> "performance".
> 
> Introduce a command-line parameter, "intel_epb=preserve", to skip the
> "performance" -> "normal" override/workaround. This maintains prior
> functionality when no parameter is set, but adds in the ability to stay at
> performance for a speedy kexec if a user wishes.
> 
> Signed-off-by: Jack Allister <jalliste@...zon.com>
> Acked-by: Rafael J. Wysocki <rafael@...nel.org>
> Cc: Paul Durrant <pdurrant@...zon.com>
> Cc: Jue Wang <juew@...zon.com>
> Cc: Usama Arif <usama.arif@...edance.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  9 ++++++++
>  arch/x86/kernel/cpu/intel_epb.c               | 22 +++++++++++++++++--
>  2 files changed, 29 insertions(+), 2 deletions(-)
> 

Reviewed-by: Paul Durrant <pdurrant@...zon.com>