From bb85fb5803270c52863b983596c2a038facaf4b3 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Mon, 3 Oct 2016 17:40:29 +1100 Subject: [PATCH] powerpc: During context switch, check before setting mm_cpumask 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 Acked-by: Balbir Singh Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/mmu_context.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h index 475d1be39191..5c451140660a 100644 --- a/arch/powerpc/include/asm/mmu_context.h +++ b/arch/powerpc/include/asm/mmu_context.h @@ -72,7 +72,8 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk) { /* Mark this context has been used on the new CPU */ - cpumask_set_cpu(smp_processor_id(), mm_cpumask(next)); + if (!cpumask_test_cpu(smp_processor_id(), mm_cpumask(next))) + cpumask_set_cpu(smp_processor_id(), mm_cpumask(next)); /* 32-bit keeps track of the current PGDIR in the thread struct */ #ifdef CONFIG_PPC32 -- 2.20.1