From: Anton Blanchard <anton@ozlabs.org>
To: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
npiggin@gmail.com, cyrilbur@gmail.com
Cc: linuxppc-dev@lists.ozlabs.org
Subject: [PATCH] powerpc: During context switch, check before setting mm_cpumask
Date: Mon, 3 Oct 2016 17:40:29 +1100 [thread overview]
Message-ID: <1475476829-6296-1-git-send-email-anton@ozlabs.org> (raw)
From: Anton Blanchard <anton@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 <anton@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
next reply other threads:[~2016-10-03 6:41 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-03 6:40 Anton Blanchard [this message]
2016-10-03 23:25 ` [PATCH] powerpc: During context switch, check before setting mm_cpumask Balbir Singh
2016-10-03 23:58 ` Benjamin Herrenschmidt
2016-10-04 0:20 ` Balbir Singh
2016-10-05 2:36 ` Michael Ellerman
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