From: Anton Blanchard <an...@samba.org>
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 <an...@samba.org>
---
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 475d1be..5c45114 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
--
2.7.4
