linux-kernel - Re: [PATCH 0/2] intel_pstate: fix turbo not being used after a processor is rebooted

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Message-ID: <mafs07cycdfh4.fsf_-_@amazon.de>
Date:   Tue, 27 Dec 2022 16:38:15 +0100
From:   Pratyush Yadav <ptyadav@...zon.de>
To:     srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
CC:     <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Len Brown" <lenb@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Robert Moore" <robert.moore@...el.com>,
        <linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devel@...ica.org>
Subject: Re: [PATCH 0/2] intel_pstate: fix turbo not being used after a
 processor is rebooted

Hi Srinivas,

On Sat, Dec 24 2022, srinivas pandruvada wrote:

> On Fri, 2022-12-23 at 10:10 -0800, srinivas pandruvada wrote:
>> Hi Pratyush,
>>
>> On Thu, 2022-12-22 at 11:39 +0100, Pratyush Yadav wrote:
>> >
>> > Hi Srinivas,
>> >
>> > On Wed, Dec 21 2022, srinivas pandruvada wrote:
>> > > On Wed, 2022-12-21 at 16:52 +0100, Pratyush Yadav wrote:
>> > > > When a processor is brought offline and online again, it is
>> > > > unable to
>> > > > use Turbo mode because the _PSS table does not contain the whole
>> > > > turbo
>> > > > frequency range, but only +1 MHz above the max non-turbo
>> > > > frequency.
>> > > > This
>> > > > causes problems when ACPI processor driver tries to set frequency
>> > > > constraints. See patch 2 for more details.
>> > > >
>> I can reproduce on a Broadwell server platform. But not on a client
>> system with acpi_ppc usage.
>>
>> Need to check what change broke this.
>
> When PPC limits enforcement changed to PM QOS, this broke. Previously
> acpi_processor_get_platform_limit() was not enforcing any limits. It
> was just setting variable. So any update done after
> acpi_register_performance_state() call to pr->performance-
>>states[ppc].core_frequency, was effective.
>
> We don't really need to call
>         ret = freq_qos_update_request(&pr->perflib_req,
>                         pr->performance->states[ppc].core_frequency *
> 1000);
>
> if the PPC is not changed. When PPC is changed, this gets called again,
> so then we can call the above function to update cpufreq limit.
>
> The below change fixed for me.

Right. Should I re-roll my patches with your diff below then? Or do you
think my patches should be good to merge as-is?

>
> diff --git a/drivers/acpi/processor_perflib.c
> b/drivers/acpi/processor_perflib.c
> index 757a98f6d7a2..c6ced89c00dd 100644
> --- a/drivers/acpi/processor_perflib.c
> +++ b/drivers/acpi/processor_perflib.c
> @@ -75,6 +75,11 @@ static int acpi_processor_get_platform_limit(struct
> acpi_processor *pr)
>         pr_debug("CPU %d: _PPC is %d - frequency %s limited\n", pr->id,
>                        (int)ppc, ppc ? "" : "not");
>
> +       if (ppc == pr->performance_platform_limit) {
> +               pr_debug("CPU %d: _PPC is %d - frequency not
> changed\n", pr->id, ppc);
> +               return 0;
> +       }
> +
>         pr->performance_platform_limit = (int)ppc;
>
>         if (ppc >= pr->performance->state_count ||
>

-- 
Regards,
Pratyush Yadav



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