Nicholas Piggin <npig...@gmail.com> writes: > On Mon, 24 Jul 2017 23:46:44 +1000 > Michael Ellerman <m...@ellerman.id.au> wrote: > >> Nicholas Piggin <npig...@gmail.com> writes: >> >> > On Mon, 24 Jul 2017 14:28:02 +1000 >> > Benjamin Herrenschmidt <b...@kernel.crashing.org> wrote: >> > >> >> Instead of comparing the whole CPU mask every time, let's >> >> keep a counter of how many bits are set in the mask. Thus >> >> testing for a local mm only requires testing if that counter >> >> is 1 and the current CPU bit is set in the mask. >> ... >> > >> > Also does it make sense to define it based on NR_CPUS > BITS_PER_LONG? >> > If it's <= then it should be similar load and compare, no? >> >> Do we make a machine with that few CPUs? ;) >> >> I don't think it's worth special casing, all the distros run with much >> much larger NR_CPUs than that. > > Not further special-casing, but just casing it based on NR_CPUS > rather than BOOK3S.
The problem is the mm_context_t is defined based on BookE vs BookS etc. not based on NR_CPUS. So we'd have to add the atomic_t to all mm_context_t's, but #ifdef'ed based on NR_CPUS. But then some platforms don't support SMP, so it's a waste there. The existing cpumask check compiles to ~= nothing on UP. cheers
