linux-kernel - Re: [PATCH v1] xen: acpi: upload

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Date:   Wed, 7 Mar 2018 12:51:12 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Joao Martins <joao.m.martins@...cle.com>,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH v1] xen: acpi: upload _PSD info for offline CPUs too

On 03/06/2018 03:12 PM, Joao Martins wrote:
> All uploaded PM data from offline CPUs takes the info from vCPU 0 and

"offline" may not be the right term here. Maybe "non-dom0"?

> changing only the acpi_id. For processors which P-state coordination type
> is HW_ALL (0xFD) it is OK to upload bogus P-state dependency information
> (_PSD), because Xen will ignore cpufreq domains existence.
>
> Albeit for hardware exposing Px coordination types as SW_ANY or SW_ALL,
> this will have some unintended side effects. Effectively, it will look at
> the P-state domain existence and *if it already exists* it will skip the
> acpi-cpufreq initialization and thus inherit the policy from the first CPU
> in the cpufreq domain. This will finally lead to the original cpu not
> changing target freq to P0 other than the first in the domain. Which will
> make turbo boost not getting enabled (e.g. for 'performance' governor) for
> all cpus.
>
> This patch fixes that, by also evaluating _PSD when enumerating all ACPI
> procesors (online and offline) and always uploading the correct P-State
> dependency up to Xen.
>
> Signed-off-by: Joao Martins <joao.m.martins@...cle.com>
> ---
> xen_processor_get_psd() is taken from acpi_processor_get_psd()
> (drivers/acpi/processor_perflib.c) simply because only Xen Dom0 needs
> to handle vcpus != pcpus. If preferred I could try exporting that API
> instead and use it here.

I think this would be a preferable approach.

-boris