[PATCH 2/2] peci-cputemp: label CPU cores from zero instead of one

Jae Hyun Yoo jae.hyun.yoo at linux.intel.com
Wed Oct 7 05:01:38 AEDT 2020

Hi Zev,

On 9/28/2020 11:00 PM, Joel Stanley wrote:
> On Mon, 28 Sep 2020 at 22:02, Zev Weiss <zev at bewilderbeest.net> wrote:
>> On Mon, Sep 28, 2020 at 04:32:31PM CDT, Jae Hyun Yoo wrote:
>>>> Oh I see -- I had thought you were referring to other existing hwmon
>>>> drivers in the kernel.
>>>> As far as I can tell, all those instances appear to be numbering CPU
>>>> *sockets* though -- which as Jason mentioned in a call earlier today
>>>> I gather is done to line up with motherboard silkscreen labeling.
>>>> But in the code in question here we're labeling *cores* within a
>>>> given socket, which I don't see arising anywhere in any existing
>>>> entity-manager configs.  So I'm still unclear on why we want to use
>>>> one-based indexing here instead of zero-based -- I'd think we'd want
>>>> the PECI driver to match the PECI spec?
>>> PECI driver uses zero-based index for PECI command handling but label is
>>> user facing stuff which shouldn't make confusion to users. We can modify
>>> driver like you did in this patch and previous driver also used
>>> zero-based indexing but I changed it to natural number based indexing
>>> to avoid confusion between driver labels and dbus-sensors names.
>>> Any specific reason for the zero-based indexing? Any benefit?
>> [Re-adding CCs...]
> Thanks. Please keep the discussion on the list.
>> Well, as I see it basically just consistency with a larger set of
>> things.  Most other related numbering schemes I'm aware of are
>> zero-based -- userspace tools like 'taskset' and 'lscpu', system APIs
>> like the <sched.h> CPU_SET() routines, and the kernel's own numbering
>> (e.g. what's shown in /proc/cpuinfo) all number processors starting from
>> zero, so dbus-sensors seems kind of like the odd one out there.
>> (Personally I'd be fully in support of changing it to be zero-based as
>> well, though I have no idea offhand about how distruptive a change that
>> would be.)
>> It also seems pretty OpenBMC-specific, whereas I'd expect we want to aim
>> for greater generality in things going into mainline.
> Agreed. The hwmon numbering varies; some attributes are zero indexed
> and some start at 1. More commonly we start counting from zero in the
> kernel, so I would expect PECI to do the same.
> If there's some userspace that depends on the behaviour of these out
> of tree PECI patches, then that userspace will need to change. This
> reminds us why the project prefers patches exposing userspace ABI are
> merged to mainline first.

Okay. Not a big deal. The coretemp module for local CPU also uses zero
starting label index for core numbers so better match up. Thanks for
your patch.

Reviewed-by: Jae Hyun Yoo <jae.hyun.yoo at linux.intel.com>

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