During context switch, switch_mm() sets our current CPU in mm_cpumask. We can avoid this atomic sequence in most cases by checking before setting the bit. Testing on a POWER8 using our context switch microbenchmark: tools/testing/selftests/powerpc/benchmarks/context_switch \ --process --no-fp --no-altivec --no-vector Performance improves 2%. Signed-off-by: Anton Blanchard <anton@samba.org> Acked-by: Balbir Singh <bsingharora@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>