linux-kernel - Re: [PATCH v1 2/6] cpufreq: intel_pstate: Do not update global.turbo

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Date: Sun, 02 Jun 2024 11:21:51 +0800
From: Xi Ruoyao <xry111@...111.site>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM
 <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Srinivas Pandruvada
	 <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v1 2/6] cpufreq: intel_pstate: Do not update
 global.turbo_disabled after initialization

On Mon, 2024-03-25 at 18:02 +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The global.turbo_disabled is updated quite often, especially in the
> passive mode in which case it is updated every time the scheduler calls
> into the driver.  However, this is generally not necessary and it adds
> MSR read overhead to scheduler code paths (and that particular MSR is
> slow to read).
> 
> For this reason, make the driver read MSR_IA32_MISC_ENABLE_TURBO_DISABLE
> just once at the cpufreq driver registration time and remove all of the
> in-flight updates of global.turbo_disabled.

Hi Rafael and Srinivas,

Thanks for the clean up, but unfortunately on one of my laptops (based
on i5-11300H) MSR_IA32_MISC_ENABLE_TURBO_DISABLE is mysteriously
changing from 1 to 0 in about one minute after system boot.  I've no
idea why this is happening (firmware is doing some stupid thing?)

I've noticed the issue before and "hacked it around"
(https://bugzilla.kernel.org/show_bug.cgi?id=218702). But after this
change I can no longer hack it around and the system is much slower.

Is it possible to hack it around again?

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University