Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread

From: Arnd Bergmann
Date: Mon Feb 29 2016 - 08:10:52 EST

On Monday 29 February 2016 12:41:49 Mathieu Desnoyers wrote:
> ----- On Feb 29, 2016, at 5:39 AM, Arnd Bergmann arnd@xxxxxxxx wrote:

> > What's making things worse is that on some architectures, adding
> > __packed will force access by bytes rather than just reading
> > a 32-bit or 64-bit numbers directly, so it's slow and non-atomic.
> Agreed that many architectures issue slower instructions when reading
> from packed structures, which is unwanted.
> Could we require that each field be naturally aligned and require that
> they are placed so _no_ padding whatsoever should ever be added by the
> compiler ? If that's possible, then we could remove the packed.

Yes, I think that is a reasonable requirement.