From dbd1b8ea43b17e2ed4acda72f83ea17f69408682 Mon Sep 17 00:00:00 2001 From: "Shreyas B. Prabhu" Date: Fri, 1 Jul 2016 09:24:14 -0500 Subject: [PATCH] cpuidle: Fix last_residency division Snooze is a poll idle state in powernv and pseries platforms. Snooze has a timeout so that if a CPU stays in snooze for more than target residency of the next available idle state, then it would exit thereby giving chance to the cpuidle governor to re-evaluate and promote the CPU to a deeper idle state. Therefore whenever snooze exits due to this timeout, its last_residency will be target_residency of the next deeper state. Commit e93e59ce5b85 "cpuidle: Replace ktime_get() with local_clock()" changed the math around last_residency calculation. Specifically, while converting last_residency value from nano- to microseconds, it carries out right shift by 10. Because of that, in snooze timeout exit scenarios last_residency calculated is roughly 2.3% less than target_residency of the next available state. This pattern is picked up by get_typical_interval() in the menu governor and therefore expected_interval in menu_select() is frequently less than the target_residency of any state other than snooze. Due to this we are entering snooze at a higher rate, thereby affecting the single thread performance. Fix this by using more precise division via ktime_us_delta(). Fixes: e93e59ce5b85 "cpuidle: Replace ktime_get() with local_clock()" Reported-by: Anton Blanchard Bisected-by: Shilpasri G Bhat Signed-off-by: Shreyas B. Prabhu Acked-by: Daniel Lezcano Acked-by: Balbir Singh Signed-off-by: Rafael J. Wysocki --- drivers/cpuidle/cpuidle.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index a4d0059e232c..c73207abb5a4 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -173,7 +173,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, struct cpuidle_state *target_state = &drv->states[index]; bool broadcast = !!(target_state->flags & CPUIDLE_FLAG_TIMER_STOP); - u64 time_start, time_end; + ktime_t time_start, time_end; s64 diff; /* @@ -195,13 +195,13 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, sched_idle_set_state(target_state); trace_cpu_idle_rcuidle(index, dev->cpu); - time_start = local_clock(); + time_start = ns_to_ktime(local_clock()); stop_critical_timings(); entered_state = target_state->enter(dev, drv, index); start_critical_timings(); - time_end = local_clock(); + time_end = ns_to_ktime(local_clock()); trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); /* The cpu is no longer idle or about to enter idle. */ @@ -217,11 +217,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, if (!cpuidle_state_is_coupled(drv, index)) local_irq_enable(); - /* - * local_clock() returns the time in nanosecond, let's shift - * by 10 (divide by 1024) to have microsecond based time. - */ - diff = (time_end - time_start) >> 10; + diff = ktime_us_delta(time_end, time_start); if (diff > INT_MAX) diff = INT_MAX; -- 2.20.1