On Wed, Jan 15, 2020 at 10:08:31AM +0100, Arnd Bergmann wrote: > > I would suggest that anybody who uses asm-generic/uaccess.h needs to > > simply use the generic library version. > > Or possibly just everybody altogether: the remaining architectures that > have a custom implementation don't seem to be doing any better either. No go for s390. There you really want to access userland memory in larger chunks - it's oriented for block transfers. IIRC, the insn they are using has a costly setup phase, independent of the amount to copy, followed by reasonably fast transfer more or less linear by the size.
