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

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Date: Sun, 02 Jun 2024 06:40:31 -0700
From: srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To: Xi Ruoyao <xry111@...111.site>, "Rafael J. Wysocki" <rjw@...ysocki.net>,
  Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/6] cpufreq: intel_pstate: Do not update
 global.turbo_disabled after initialization

On Sun, 2024-06-02 at 12:25 +0800, Xi Ruoyao wrote:
> On Sat, 2024-06-01 at 21:03 -0700, srinivas pandruvada wrote:
> > Hi Xi,
> > 
> > On Sun, 2024-06-02 at 11:21 +0800, Xi Ruoyao wrote:
> > > 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?
> > > 
> > Please try the attached diff and build kernel and try.
> > 
> > git apply update_max_freq.diff
> > 
> > Then build kernel and install.
> 
> Unfortunately it didn't work.  Then I tried:
> 
> @@ -1304,6 +1310,10 @@ static ssize_t store_no_turbo(struct kobject
> *a, struct kobj_attribute *b,
>         if (no_turbo == global.no_turbo)
>                 goto unlock_driver;
>  
> +       global.turbo_disabled = turbo_is_disabled();
> +       global.no_turbo = global.turbo_disabled;
> +       arch_set_max_freq_ratio(global.turbo_disabled);
> +
>         if (global.turbo_disabled) {
>                 pr_notice_once("Turbo disabled by BIOS or unavailable
> on processor\n");
>                 count = -EPERM;
> 
> and my old hack worked again.  Curiously after I writing 0 to
> /sys/devices/system/cpu/intel_pstate/no_turbo successfully, your code
> is
> triggered.
> 
> $ dmesg | grep intel_pstate
> [    0.554425] intel_pstate: Intel P-state driver initializing
> [    0.554877] intel_pstate: HWP enabled
> [    1.780021] intel_pstate: Turbo disabled by BIOS or unavailable on
> processor
> [   21.789044] intel_pstate: intel_pstate_update_limits cpu:0
> [   21.789053] intel_pstate: intel_pstate_update_limits cpu:1
> [   21.789060] intel_pstate: intel_pstate_update_limits cpu:2
> [   21.789189] intel_pstate: intel_pstate_update_limits cpu:3
> [   21.789198] intel_pstate: intel_pstate_update_limits cpu:4
> [   21.789203] intel_pstate: intel_pstate_update_limits cpu:5
> [   21.789209] intel_pstate: intel_pstate_update_limits cpu:6
> [   21.789276] intel_pstate: intel_pstate_update_limits cpu:7
> 
> The message at [1.780021] is from the first attempt writing 0 to
> /sys/devices/system/cpu/intel_pstate/no_turbo when
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE is still 1

This requires user action,
Please add a
pr_info() to
https://elixir.bootlin.com/linux/v6.10-rc1/C/ident/acpi_processor_notify

Check if you got any message

Also what is 
cat /proc/cpuinfo
and
cpuid -1

Thanks,
Srinivas