From b5fda7ed5c63297d0f43e608b455d82ceabdebf0 Mon Sep 17 00:00:00 2001 From: Jisheng Zhang Date: Fri, 25 Mar 2016 11:08:55 +0800 Subject: [PATCH] arm64: cpuidle: make arm_cpuidle_suspend() a bit more efficient Currently, we check two pointers: cpu_ops and cpu_suspend on every idle state entry. These pointers check can be avoided: If cpu_ops has not been registered, arm_cpuidle_init() will return -EOPNOTSUPP, so arm_cpuidle_suspend() will never have chance to run. In other word, the cpu_ops check can be avoid. Similarly, the cpu_suspend check could be avoided in this hot path by moving it into arm_cpuidle_init(). I measured the 4096 * time from arm_cpuidle_suspend entry point to the cpu_psci_cpu_suspend entry point. HW platform is Marvell BG4CT STB board. 1. only one shell, no other process, hot-unplug secondary cpus, execute the following cmd while true do sleep 0.2 done before the patch: 1581220ns after the patch: 1579630ns reduced by 0.1% 2. only one shell, no other process, hot-unplug secondary cpus, execute the following cmd while true do md5sum /tmp/testfile sleep 0.2 done NOTE: the testfile size should be larger than L1+L2 cache size before the patch: 1961960ns after the patch: 1912500ns reduced by 2.5% So the more complex the system load, the bigger the improvement. Signed-off-by: Jisheng Zhang Acked-by: Lorenzo Pieralisi Signed-off-by: Will Deacon --- arch/arm64/kernel/cpuidle.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c index 9047cab68fd3..e11857fce05f 100644 --- a/arch/arm64/kernel/cpuidle.c +++ b/arch/arm64/kernel/cpuidle.c @@ -19,7 +19,8 @@ int __init arm_cpuidle_init(unsigned int cpu) { int ret = -EOPNOTSUPP; - if (cpu_ops[cpu] && cpu_ops[cpu]->cpu_init_idle) + if (cpu_ops[cpu] && cpu_ops[cpu]->cpu_suspend && + cpu_ops[cpu]->cpu_init_idle) ret = cpu_ops[cpu]->cpu_init_idle(cpu); return ret; @@ -36,11 +37,5 @@ int arm_cpuidle_suspend(int index) { int cpu = smp_processor_id(); - /* - * If cpu_ops have not been registered or suspend - * has not been initialized, cpu_suspend call fails early. - */ - if (!cpu_ops[cpu] || !cpu_ops[cpu]->cpu_suspend) - return -EOPNOTSUPP; return cpu_ops[cpu]->cpu_suspend(index); } -- 2.20.1