linux-kernel - Re: [PATCH V12 4/7] cpufreq: Add a notification message that the highest perf has changed

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Message-ID: <CAJZ5v0iriUv8ZMLYz43AB88rQL2DdP3Wn8WwF00XWhZyce+eYw@mail.gmail.com>
Date: Wed, 27 Dec 2023 18:03:48 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "Meng, Li (Jassmine)" <Li.Meng@....com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, 
	"Huang, Ray" <Ray.Huang@....com>, "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, 
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>, Shuah Khan <skhan@...uxfoundation.org>, 
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>, 
	"Fontenot, Nathan" <Nathan.Fontenot@....com>, "Sharma, Deepak" <Deepak.Sharma@....com>, 
	"Deucher, Alexander" <Alexander.Deucher@....com>, 
	"Limonciello, Mario" <Mario.Limonciello@....com>, "Huang, Shimmer" <Shimmer.Huang@....com>, 
	"Yuan, Perry" <Perry.Yuan@....com>, "Du, Xiaojian" <Xiaojian.Du@....com>, 
	Viresh Kumar <viresh.kumar@...aro.org>, Borislav Petkov <bp@...en8.de>, 
	Oleksandr Natalenko <oleksandr@...alenko.name>
Subject: Re: [PATCH V12 4/7] cpufreq: Add a notification message that the
 highest perf has changed

On Wed, Dec 27, 2023 at 2:40 AM Meng, Li (Jassmine) <Li.Meng@....com> wrote:
>
> [AMD Official Use Only - General]
>
> Hi Rafael:
>
> > -----Original Message-----
> > From: Meng, Li (Jassmine)
> > Sent: Tuesday, December 26, 2023 4:27 PM
> > To: Rafael J. Wysocki <rafael@...nel.org>
> > Cc: Rafael J . Wysocki <rafael.j.wysocki@...el.com>; Huang, Ray
> > <Ray.Huang@....com>; linux-pm@...r.kernel.org; linux-
> > kernel@...r.kernel.org; x86@...nel.org; linux-acpi@...r.kernel.org; Shuah
> > Khan <skhan@...uxfoundation.org>; linux-kselftest@...r.kernel.org;
> > Fontenot, Nathan <Nathan.Fontenot@....com>; Sharma, Deepak
> > <Deepak.Sharma@....com>; Deucher, Alexander
> > <Alexander.Deucher@....com>; Limonciello, Mario
> > <Mario.Limonciello@....com>; Huang, Shimmer
> > <Shimmer.Huang@....com>; Yuan, Perry <Perry.Yuan@....com>; Du,
> > Xiaojian <Xiaojian.Du@....com>; Viresh Kumar <viresh.kumar@...aro.org>;
> > Borislav Petkov <bp@...en8.de>; Oleksandr Natalenko
> > <oleksandr@...alenko.name>
> > Subject: RE: [PATCH V12 4/7] cpufreq: Add a notification message that the
> > highest perf has changed
> >
> > Hi Rafael:
> >
> > > -----Original Message-----
> > > From: Rafael J. Wysocki <rafael@...nel.org>
> > > Sent: Tuesday, December 12, 2023 9:44 PM
> > > To: Meng, Li (Jassmine) <Li.Meng@....com>
> > > Cc: Rafael J . Wysocki <rafael.j.wysocki@...el.com>; Huang, Ray
> > > <Ray.Huang@....com>; linux-pm@...r.kernel.org; linux-
> > > kernel@...r.kernel.org; x86@...nel.org; linux-acpi@...r.kernel.org;
> > > Shuah Khan <skhan@...uxfoundation.org>;
> > > linux-kselftest@...r.kernel.org; Fontenot, Nathan
> > > <Nathan.Fontenot@....com>; Sharma, Deepak
> > <Deepak.Sharma@....com>;
> > > Deucher, Alexander <Alexander.Deucher@....com>; Limonciello, Mario
> > > <Mario.Limonciello@....com>; Huang, Shimmer
> > <Shimmer.Huang@....com>;
> > > Yuan, Perry <Perry.Yuan@....com>; Du, Xiaojian
> > <Xiaojian.Du@....com>;
> > > Viresh Kumar <viresh.kumar@...aro.org>; Borislav Petkov
> > > <bp@...en8.de>; Oleksandr Natalenko <oleksandr@...alenko.name>
> > > Subject: Re: [PATCH V12 4/7] cpufreq: Add a notification message that
> > > the highest perf has changed
> > >
> > > Caution: This message originated from an External Source. Use proper
> > > caution when opening attachments, clicking links, or responding.
> > >
> > >
> > > On Wed, Dec 6, 2023 at 10:13 PM Rafael J. Wysocki <rafael@...nel.org>
> > > wrote:
> > > >
> > > > On Wed, Dec 6, 2023 at 9:58 PM Rafael J. Wysocki <rafael@...nel.org>
> > > wrote:
> > > > >
> > > > > On Tue, Dec 5, 2023 at 7:38 AM Meng Li <li.meng@....com> wrote:
> > > > > >
> > > > > > ACPI 6.5 section 8.4.6.1.1.1 specifies that Notify event 0x85
> > > > > > can be emmitted to cause the the OSPM to re-evaluate the highest
> > > > > > performance
> > > > >
> > > > > Typos above.  Given the number of iterations of this patch, this
> > > > > is kind of disappointing.
> > > > >
> > > > > > register. Add support for this event.
> > > > >
> > > > > Also it would be nice to describe how this is supposed to work at
> > > > > least roughly, so it is not necessary to reverse-engineer the
> > > > > patch to find out that.
> > > > >
> > > > > > Tested-by: Oleksandr Natalenko <oleksandr@...alenko.name>
> > > > > > Reviewed-by: Mario Limonciello <mario.limonciello@....com>
> > > > > > Reviewed-by: Huang Rui <ray.huang@....com>
> > > > > > Reviewed-by: Perry Yuan <perry.yuan@....com>
> > > > > > Signed-off-by: Meng Li <li.meng@....com>
> > > > > > Link:
> > > > > >
> > > https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model
> > > > > > .html#processor-device-notification-values
> > > > > > ---
> > > > > >  drivers/acpi/processor_driver.c |  6 ++++++
> > > > > >  drivers/cpufreq/cpufreq.c       | 13 +++++++++++++
> > > > > >  include/linux/cpufreq.h         |  5 +++++
> > > > > >  3 files changed, 24 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/acpi/processor_driver.c
> > > > > > b/drivers/acpi/processor_driver.c index
> > > > > > 4bd16b3f0781..29b2fb68a35d
> > > > > > 100644
> > > > > > --- a/drivers/acpi/processor_driver.c
> > > > > > +++ b/drivers/acpi/processor_driver.c
> > > > > > @@ -27,6 +27,7 @@
> > > > > >  #define ACPI_PROCESSOR_NOTIFY_PERFORMANCE 0x80
> > > > > >  #define ACPI_PROCESSOR_NOTIFY_POWER    0x81
> > > > > >  #define ACPI_PROCESSOR_NOTIFY_THROTTLING       0x82
> > > > > > +#define ACPI_PROCESSOR_NOTIFY_HIGEST_PERF_CHANGED
> > 0x85
> > > > > >
> > > > > >  MODULE_AUTHOR("Paul Diefenbaugh");
> > > MODULE_DESCRIPTION("ACPI
> > > > > > Processor Driver"); @@ -83,6 +84,11 @@ static void
> > > > > > acpi_processor_notify(acpi_handle handle, u32 event, void *data)
> > > > > >                 acpi_bus_generate_netlink_event(device->pnp.device_class,
> > > > > >                                                   dev_name(&device->dev), event, 0);
> > > > > >                 break;
> > > > > > +       case ACPI_PROCESSOR_NOTIFY_HIGEST_PERF_CHANGED:
> > > > > > +               cpufreq_update_highest_perf(pr->id);
> > > > >
> > > > > And the design appears to be a bit ad-hoc here.
> > > > >
> > > > > Because why does it have anything to do with cpufreq?
> > > >
> > > > Well, clearly, cpufreq can be affected by this, but why would it be
> > > > not affected the same way as in the
> > > ACPI_PROCESSOR_NOTIFY_PERFORMANCE
> > > > case?
> > > >
> > > > That is, why isn't cpufreq_update_limits() the right thing to do?
> > >
> > > Seriously, I'm not going to apply this patch so long as my comments
> > > above are not addressed.
> > [Meng, Li (Jassmine)]
> > Sorry for the delayed reply to the email.
> > BIOS/AGESA is responsible to issue the Notify 0x85 to OS that the preferred
> > core has changed.
> > It will only affect the ranking of the preferred core, not the impact policy
> > limits.
> > AMD P-state driver will set the priority of the cores based on the preferred
> > core ranking, and prioritize selecting higher priority core to run the task.
> [Meng, Li (Jassmine)]
> From ACPI v6.5, Table 5.197 Processor Device Notification Values:
> Hex value               Description
> 0x80                    Performance Present Capabilities Changed. Used to notify OSPM that the number of supported processor performance states has changed. This notification causes OSPM to re-evaluate the _PPC object. See Section 8.4.5.3 for more information.
>
> 0x85                    Highest Performance Changed. Used to notify OSPM that the value of the CPPC Highest Performance Register has changed.
>
> I think they are different notify events, so they need different functions to handle these events.

But they effectively mean pretty much the same thing: the highest
available performance state of the CPU has changed.

Why would the response need to be different?