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

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Message-ID: <CAJZ5v0jNB1UnwW8mW6Cu9qi4vdvH9twMRkGcSOcndv_SEDeoOA@mail.gmail.com>
Date:   Tue, 27 Dec 2022 17:15:04 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Pratyush Yadav <ptyadav@...zon.de>
Cc:     linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        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

On Wed, Dec 21, 2022 at 4:52 PM Pratyush Yadav <ptyadav@...zon.de> 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.

That's because of the way P-state limits in the turbo range are
handled by the given processor.

Some of them restrict the P-state even if the limit is located within
the turbo range and some of them don't (that is, requesting any
P-state in the turbo range gives the processor a license to use the
whole of it).

> This causes problems when ACPI processor driver tries to set frequency
> constraints.

The problem is that acpi_processor_get_platform_limit() sets the limit
to the frequency for all of the _PSS states including the last special
one and it should update the QoS to "no limit" in that case.