riscv: enable HAVE_FAST_GUP if MMU
Activate the fast gup for riscv mmu platforms. Here are some
GUP_FAST_BENCHMARK performance numbers:
Before the patch:
GUP_FAST_BENCHMARK: Time: get:53203 put:5085 us
After the patch:
GUP_FAST_BENCHMARK: Time: get:17711 put:5060 us
The get time is reduced by 66.7%! IOW, 3x get speed!
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20231219175046.2496-5-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>