linux-kernel - Re: [PATCH v1 0/6] intel_pstate: Turbo disabled handling rework

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Message-ID: <2a3e223f3f248e8b02a8aeb47ab2ab15a6225889.camel@linux.intel.com>
Date: Tue, 02 Apr 2024 01:46:04 -0700
From: srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM
 <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 0/6] intel_pstate: Turbo disabled handling rework

On Mon, 2024-03-25 at 18:00 +0100, Rafael J. Wysocki wrote:
> Hi Everyone,
> 
> This series reworks the handling of disabling turbo in intel_pstate
> on top of the previous series of cleanups
> 
> https://lore.kernel.org/linux-pm/12409658.O9o76ZdvQC@kreacher/
> 
> The underlying problem is that disabling turbo is handled quite
> consistently
> in intel_pstate and basically it can get disabled at any time
> (through
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE) without much coordination with
> the
> cpufreq core or anything else.
> 
> Disabling turbo through the "no_turbo" sysfs attribute is more
> consistent,
> but it has issues too (for example, if turbo is disabled via
> "no_turbo",
> the frequency-invariance code gets notified on the turbo status
> change,
> but the actual maximum frequency of the CPU is only updated if the
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE value changes either, which need
> not
> happen at the same time or even at all).
> 
> The first patch is not really related to the rest of the series, it's
> just a cleanup and can be applied separately.
> 
> Patch [2/6] uses the observation that it should be necessary to read
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE after driver initialization to
> remove
> in-flight reads on that MSR and turbo state updates related to them.
> 
> Patch [3/6] builds on top of the previous one to adjust the
> "no_turbo"
> attribute "store" and "show" callbacks.
> 
> Patch [4/6] adds READ_ONCE() annotations to global.no_turbo accesses
> and
> makes some related simplifications.
> 
> Patch [5/6] replaces the cached MSR_IA32_MISC_ENABLE_TURBO_DISABLE
> value in some checks with global.no_turbo for consistency.
> 
> Patch [6/6] makes all of the code paths where the maximum CPU
> frequency
> can change to do that consistently by using the same set of
> functions.
> 
> Details are described in the individual patch changelogs.
> 

Acked-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>

Thanks,
Srinivas

> Thanks!
> 
> 
> 
>