| Message ID | 1467013336-19966-2-git-send-email-zhaoyang.huang@spreadtrum.com (mailing list archive) |
|---|---|
| State | RFC, archived |
| Headers | show |
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 536ada8..ee3be3d 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -975,6 +975,11 @@ void tick_nohz_irq_exit(void) ktime_t tick_nohz_get_sleep_length(void) { struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); + struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); + ktime_t now; + + now = ktime_get(); + ts->sleep_length = ktime_sub(dev->next_event, now); return ts->sleep_length; }
As shown in bellowing chart, there should be a gap between tick_nohz_idle_enter(step '1') and tick_nohz_get_sleep_length (step '3') when idle, which comprise of the execution time of the code behind step '1' and a series of notify call(step2,4). Yes, for most of the scenarios, it would NOT be a problem. However,all time consumed by the steps above will cause the sleep_length is not very precised in the scenario where the idle state is shallow(imagin an idle state last less than 500us under a 200Mhz's P-state). Change it in this series of patch. Please refer to bellowing chart for detailed information current approach: static void cpu_idle_loop(void) { while (1) { tick_nohz_idle_enter(); --->__tick_nohz_idle_enter --->tick_nohz_stop_sched_tick { ... ts->sleep_length = ktime_sub(dev->next_event, now); /*1*/ ... } while (!need_resched()) { ... local_irq_disable(); arch_cpu_idle_enter(); --->idle_notifier_call_chain(IDLE_START); /*2*/ cpuidle_idle_call(); --->next_state = cpuidle_select(drv, dev); /*3*/ --->static int arm_enter_idle_state(...) { ... ret = cpu_pm_enter(); /*4*/ } } ---------|----------------------|----------------------------|------------------------------------|--------------------------------------------|-------------------- 1.now 2.IDLE_START 3.select idle state 4.CPU_PM_ENTER next_event (sleep_length) modified approach: static void cpu_idle_loop(void) { while (1) { tick_nohz_idle_enter(); --->__tick_nohz_idle_enter --->tick_nohz_stop_sched_tick { ... ... } while (!need_resched()) { ... local_irq_disable(); arch_cpu_idle_enter(); --->idle_notifier_call_chain(IDLE_START); /*1*/ cpuidle_idle_call(); --->ret = cpu_pm_enter(); /*2*/ --->tick_nohz_get_sleep_length { ts->sleep_length = ktime_sub(dev->next_event, now); /*3*/ } --->next_state = cpuidle_select(drv, dev); /*4*/ --->static int arm_enter_idle_state(...) } ----------------|---------------------------------------|---------------------|------------------|--------------------------------------------|-------------------- 1.IDLE_START 2.CPU_PM_ENTER 3.now 4.select idle state next_event (sleep_length) Signed-off-by: Zhaoyang Huang <zhaoyang.huang@spreadtrum.com> --- kernel/time/tick-sched.c | 5 +++++ 1 file changed, 5 insertions(+)