Subject: [PATCHv4 5/5] arm64: cpuinfo: print info for all CPUs

From: [email-masked] (Catalin Marinas)
Date: Thu, 17 Jul 2014 18:10:58 +0100

On Thu, Jul 17, 2014 at 02:55:37PM +0100, Peter Maydell wrote:
> On 17 July 2014 13:35, Will Deacon <[email-masked]> wrote:
> > We're not denying the possibility of heterogeneity, we're trying to expose a
> > consistent view of the system to userspace. Differences between cores should
> > be dealt with by the kernel (e.g. IKS, HMP scheduling), not blindly
> > passed off to userspace.
> 
> On that basis, why report anything at all about invididual cores?
> Just have /proc/cpuinfo report "number of processors: 4" and
> no per-CPU information at all...

We lost a lot of time on this already (given the internal threads). So
my proposal is to go ahead with Mark's patch with per-CPU features. They
currently just include the same elf_hwcap multiple times. If we ever
need to present different features, the conditions would be:

1. Never report more than elf_hwcap
2. elf_hwcap can only include non-symmetric features *if* Linux gets a
   way to transparently handle migration or emulation

It basically means that Linux would not rely on the user space to make
informed decisions on where to run a thread and avoid SIGILL.

-- 
Catalin