Re: [PATCH v2 05/13] powerpc: use linux/unaligned/le_struct.h on LE power7

Segher Boessenkool
2021-05-14T11:53:48Z

Hi Arnd,

On Fri, May 14, 2021 at 12:00:53PM +0200, Arnd Bergmann wrote:
> Little-endian POWER7 kernels disable
> CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS because that is not supported on
> the hardware, but the kernel still uses direct load/store for explicti
> get_unaligned()/put_unaligned().
>
> I assume this is a mistake that leads to power7 having to trap and fix
> up all these unaligned accesses at a noticeable performance cost.
>
> The fix is completely trivial, just remove the file and use the
> generic version that gets it right.

LE p7 isn't supported (it requires special firmware), and no one uses it
anymore, also not for development. It was used for powerpc64le-linux
development before p8 was widely available.

Segher