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

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Date: Tue, 4 Jun 2024 18:46:53 +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 Tue, Jun 4, 2024 at 6:41 PM srinivas pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> On Tue, 2024-06-04 at 18:32 +0800, Xi Ruoyao wrote:
> > On Tue, 2024-06-04 at 03:29 -0700, srinivas pandruvada wrote:
> > > On Tue, 2024-06-04 at 17:30 +0800, Xi Ruoyao wrote:
> > > > On Mon, 2024-06-03 at 21:31 -0700, srinivas pandruvada wrote:
> > > >
> > > > > > > Second, a delayed work can be added to check the MSR long
> > > > > > > enough
> > > > > > > after
> > > > > > > initialization and update global.turbo_disabled if it is 1.
> > > > > > > However,
> > > > > > > that would require some code surgery.
> > > > > >
> > > > > Something like the attached which does same way as user space
> > > > > no_turbo
> > > > > update.
> > > >
> > > > >  static int intel_pstate_register_driver(struct cpufreq_driver
> > > > > *driver)
> > > > >  {
> > > > >         int ret;
> > > > > @@ -3114,6 +3137,9 @@ static int
> > > > > intel_pstate_register_driver(struct cpufreq_driver *driver)
> > > > >         global.turbo_disabled = turbo_is_disabled();
> > > > >         global.no_turbo = global.turbo_disabled;
> > > > >
> > > > > +       if (global.turbo_disabled)
> > > > > +               schedule_delayed_work(&turbo_work, HZ);
> > > > > +
> > > >
> > > > I have to change it to 20 * HZ to make it work for me.  15 * HZ
> > > > does
> > > > not
> > > > work.
> > >
> > > Is there any consistency or it is changing every time?
> >
> > It seems consistent.
> With such a delay, I am not sure how this even worked before.
> Can you revert the patch in question and use kernel dynamic debug
> dyndbg="file intel_pstate.c +p" kernel command line and collect log for
> 30 seconds?

I think that it worked because the MSR was read every time
intel_pstate ran, so it got updated at one point and stayed that way.