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 <[email protected]>
Acked-by: Lorenzo Pieralisi <[email protected]>
---
Since v1:
- add performance numbers
- combine two small patches into one
- add Lorenzo's ack
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 9047cab6..e11857f 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);
}
--
2.8.0.rc3