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Message-ID: <6ebadacd8aaa307a5766cdb1b4d4a5c69acd87ac.camel@xry111.site>
Subject: Re: [PATCH v1 2/6] cpufreq: intel_pstate: Do not update
 global.turbo_disabled after initialization
From: Xi Ruoyao <xry111@xry111.site>
To: srinivas pandruvada <srinivas.pandruvada@linux.intel.com>, "Rafael J.
 Wysocki" <rjw@rjwysocki.net>, Linux PM <linux-pm@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Date: Sun, 02 Jun 2024 12:25:01 +0800
In-Reply-To: <6d5ee74605bd9574baa5ed111cb54e959414437a.camel@linux.intel.com>
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	 <6d5ee74605bd9574baa5ed111cb54e959414437a.camel@linux.intel.com>
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On Sat, 2024-06-01 at 21:03 -0700, srinivas pandruvada wrote:
> Hi Xi,
>=20
> 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@intel.com>
> > >=20
> > > 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.=C2=A0 However, this is generally not necessary and i=
t
> > > adds
> > > MSR read overhead to scheduler code paths (and that particular MSR
> > > is
> > > slow to read).
> > >=20
> > > 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.
> >=20
> > Hi Rafael and Srinivas,
> >=20
> > 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.=C2=A0 I've =
no
> > idea why this is happening (firmware is doing some stupid thing?)
> >=20
> > I've noticed the issue before and "hacked it around"
> > (https://bugzilla.kernel.org/show_bug.cgi?id=3D218702). But after this
> > change I can no longer hack it around and the system is much slower.
> >=20
> > Is it possible to hack it around again?
> >=20
> Please try the attached diff and build kernel and try.
>=20
> git apply update_max_freq.diff
>=20
> 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, str=
uct kobj_attribute *b,
 	if (no_turbo =3D=3D global.no_turbo)
 		goto unlock_driver;
=20
+	global.turbo_disabled =3D turbo_is_disabled();
+	global.no_turbo =3D 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 =3D -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 proce=
ssor
[   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.

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University