On Wed, Jun 21, 2017 at 4:09 AM, Paolo Abeni <pab...@redhat.com> wrote: > > + if (len <= 64) > + return copy_user_generic_unrolled(to, from, len); > + > /* > * If CPU has ERMS feature, use copy_user_enhanced_fast_string. > * Otherwise, if CPU has rep_good feature, use > copy_user_generic_string.
NAK. Please do *not* do this. It puts the check in completely the wrong place for several reasons: (a) it puts it in the inlined caller case (which could be ok for constant sizes, but not in general) (b) it uses the copy_user_generic_unrolled() function that will then just test the size *AGAIN* against small cases. so it's both bigger than necessary, and stupid. So if you want to do this optimization, I'd argue that you should just do it inside the copy_user_enhanced_fast_string() function itself, the same way we already handle the really small case specially in copy_user_generic_string(). And do *not* use the unrolled code, which isn't used for small copies anyway - rewrite the "copy_user_generic_unrolled" function in that same asm file to have the non-unrolled cases (label "17" and forward) accessible, so that you don't bother re-testing the size. Linus