Questions about /proc/cpuinfo for arch-ARM - CAS-149046-Y1H3T8

Marc Zyngier maz at kernel.org
Mon Jan 20 01:41:59 PST 2020


Hi Steven,

On 2020-01-20 10:24, Steven Miao wrote:
> CC arm mailing list. Someone know the whole history may have a better 
> answer.
> 
> Thanks,
> Steven
> 
> From: Support-Software <mailto:support-software at arm.com>
> Sent: Monday, January 20, 2020 5:17 PM
> To: Tao Zeng <mailto:prime.zeng at hisilicon.com>
> Cc: Mark Rutland <mailto:Mark.Rutland at arm.com>
> Subject: Re: Questions about /proc/cpuinfo for arch-ARM - 
> CAS-149046-Y1H3T8
> 
> From Steven Miao - Arm Partner Enablement Group
> Please quote case reference number
> https://support.developer.arm.com/case-details/?id=f9beb263-333b-ea11-a813-000d3ab4f2f3
> in any further emails to us on this subject.
> 
> Hi Tao,
>> 1. Since /proc/cpuinfo is treated as ABI, so where can I find the 
>> specification? Or is there any docs
>> to describe the details? Or it is just some applications who have 
>> already token it?
>  I think it is just de-facto ABI legacy application are relying on,
> there's no such specification.
>> You know that, in x86, /proc/cpuinfo provide really good user 
>> experience,
>> what we want to do is providing the same or even better user 
>> experience.

Tao: And by "better user experience", you mean breaking existing 
software?
I'm sure users will enjoy the "improvement".

> We should add new stuff to /sys/, don't add new things to /proc. On
> x86 these strings are acquired from the CPU itself, via CPUID
> instructions, which means that it works for future CPUs. For ARM
> systems, we have no consistent way of acquiring a model name from a
> CPU itself. If users who want to decode MIDRs are going to have to use
> userspace tools.
> Changing current cpuinfo:
> - it breaks existing applications
> - it is unmaintainable in the long run
> - we can already get cpu information by dmidecode, lscpu, lshw...

Exactly. The subject has been rehashed to death, and is not up for
discussion anymore. /proc/cpuinfo is ABI, which means its format is
forever immutable. Userspace has all the required tools at its disposal.

         M.
-- 
Jazz is not dead. It just smells funny...



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