On Wed, Nov 21, 2018 at 9:27 AM Linus Torvalds <torva...@linux-foundation.org> wrote: > > It would be interesting to know exactly which copy it is that matters > so much... *inlining* the erms case might show that nicely in > profiles.
Side note: the fact that Jens' patch (which I don't like in that form) allegedly shrunk the resulting kernel binary would seem to indicate that there's a *lot* of compile-time constant-sized memcpy calls that we are missing, and that fall back to copy_user_generic(). It might be interesting to just change raw_copy_to/from_user() to handle a lot more cases (in particular, handle cases where 'size' is 8-byte aligned). The special cases we *do* have may not be the right ones (the 10-byte case in particular looks odd). For example, instead of having a "if constant size is 8 bytes, do one get/put_user()" case, we might have a "if constant size is < 64 just unroll it into get/put_user()" calls. Linus