Messages in this thread Patch in this message | | | Subject | Re: [RFC PATCH v2 5/8] timers: keep sleep length updated as needed | From | "Li, Aubrey" <> | Date | Mon, 16 Oct 2017 14:46:41 +0800 |
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On 2017/10/14 8:56, Rafael J. Wysocki wrote: > On Saturday, September 30, 2017 9:20:31 AM CEST Aubrey Li wrote: >> sleep length indicates how long we'll be idle. Currently, it's updated >> only when tick nohz enters. These patch series make a new requirement >> with tick, so we should keep sleep length updated as needed > > So what exactly would be the problem with leaving things as they are?
Previously ts->sleep_length is only updated when tick is stopped.
As follows, in
__tick_nohz_idle_enter() { if (can_stop_idle_tick() /* return true */) { tick_nohz_stop_sched_tick() | |-----> update sleep_length } }
Now ts->sleep_length is required out of tick_nohz_idle_enter(), so we want to update sleep_length every time we read it
If we leave it unchanged, the prediction could read a sleep_length long time ago if the system keep ticking. > >> --- >> kernel/time/tick-sched.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c >> index d663fab..94fb9b8 100644 >> --- a/kernel/time/tick-sched.c >> +++ b/kernel/time/tick-sched.c >> @@ -1008,8 +1008,11 @@ void tick_nohz_irq_exit(void) >> */ >> ktime_t tick_nohz_get_sleep_length(void) >> { >> + struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); >> struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); >> >> + ts->sleep_length = ktime_sub(dev->next_event, ktime_get()); >> + >> return ts->sleep_length; >> } >> >> > > I probably wouldn't do it this way ... > >
May I know the detailed thoughts?
Thanks, -Aubrey
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