Re: [PATCH] x86/uaccess: optimize copy_user_enhanced_fast_string for short string

[Linus Torvalds]

Looks ok to me, so Ack, fwiw.

I've have long hoped that Intel would actually fix their microcode
overhead issue so that we could get rid of all this and just inline
"rep movsb", but that hasn't been happening, so this patch looks fine.

Side niote: I suspect the copy_user_generic_string() might as well use
the same logic too, rather than having a different cut-off (8 bytes)
to a worse implementation (rep movsb on architectures that don't mark
themselves with the enhanced string).

                  Linus

On Thu, Jun 29, 2017 at 6:55 AM, Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
> According to the Intel datasheet, the rep movsb instruction
> exposes a relevant setup cost - 50 ticks - which affect
> badly short string copy operation.