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

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Date: Fri, 7 Jun 2024 17:04:56 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: Xi Ruoyao <xry111@...111.site>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/6] cpufreq: intel_pstate: Do not update
 global.turbo_disabled after initialization

On Wed, Jun 5, 2024 at 2:05 PM srinivas pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> On Wed, 2024-06-05 at 13:21 +0800, Xi Ruoyao wrote:
> > On Tue, 2024-06-04 at 09:56 -0700, srinivas pandruvada wrote:
> > > > > With such a delay, I am not sure how this even worked before.
> >
> > It didn't work out of box but it worked after manually writing 0 to
> > no_turbo after 20 seconds, see
> > https://bugzilla.kernel.org/show_bug.cgi?id=218702.
>
> That make sense. So it never worked out of box. The store_no_turbo()
> has additional read for turbo flag before, which is removed now. I
> think adding that back will will restore old behavior.
>
> diff --git a/drivers/cpufreq/intel_pstate.c
> b/drivers/cpufreq/intel_pstate.c
> index 4b986c044741..0d5330e5b96b 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1301,6 +1301,8 @@ static ssize_t store_no_turbo(struct kobject *a,
> struct kobj_attribute *b,
>
>         no_turbo = !!clamp_t(int, input, 0, 1);
>
> +       global.turbo_disabled = turbo_is_disabled();
> +
>         if (no_turbo == global.no_turbo)
>                 goto unlock_driver;
>
>
> Need to adjust the mutex around it also.

Anyhow, it can be made work.

global.turbo_disabled can be updated right before it is checked in
store_no_turbo(), so if 0 is written to no_turbo (and global.no_turbo
is 1), it will succeed if global.turbo_disabled changes from 1 to 0.

Something like the attached (untested) patch.

View attachment "intel_pstate-turbo_disabled.patch" of type "text/x-patch" (1506 bytes)