Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v1] xen: acpi: upload _PSD info for offline CPUs too
To:     Joao Martins <joao.m.martins@oracle.com>,
        linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org
Cc:     Juergen Gross <jgross@suse.com>
References: <20180306201209.21890-1-joao.m.martins@oracle.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <a62621c6-ca44-fae4-7661-b7fe5380bbc0@oracle.com>
Date:   Wed, 7 Mar 2018 12:51:12 -0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <20180306201209.21890-1-joao.m.martins@oracle.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@oracle.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