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

On Monday 29 February 2016 12:41:49 Mathieu Desnoyers wrote:

----- On Feb 29, 2016, at 5:39 AM, Arnd Bergmann arnd-r2nGTMty4D4@public.gmane.org wrote:

quoted

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.

	Arnd