Re: x86: faster strncpy_from_user()

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2012-04-06 at 14:32 -0700, Linus Torvalds wrote:
> Ok, as some of you are aware, one of the things that got merged very
> early in the 3.4 merge window was the "word-at-a-time" filename lookup
> patches I had been working on. They only get enabled on x86, but when
> they do, they do speed things up by quite a noticeable bit (mainly on
> x86-64, which ends up doing things 8 bytes at a time - it's much less
> noticeable on x86-32).

Talking of which ... I haven't had much time to look but any reason that
wouldn't work on BE platforms as well when they have a fast
byteswap-load ? Now powerpc sadly only have up to 32-bit byteswap loads
so doing 64-bit requires a bit of shifting around but the result might
still be faster than loading individual bytes especially since we do
have a bunch of registers to spare....

Something lines of

-		a = *(unsigned long *)name;
+		a = le64_to_cpup((__le64 *)name);

(etc...)

Maybe ?

I might have a chance to actually test later today (chasing some
regressions goes first)

Cheers,
Ben.