On Mon, Apr 21, 2014 at 03:25:10PM +0530, Viresh Kumar wrote: > The sequence of calls for dynticks CPUs is a bit confusing. Add a comment in > tick_nohz_idle_exit() to mention it clearly. All information required is in > commit and this conversation with Frederic. > > https://lkml.org/lkml/2014/4/10/355 > > Suggested-by: Frederic Weisbecker <fweis...@gmail.com> > Signed-off-by: Viresh Kumar <viresh.ku...@linaro.org> > --- > kernel/time/tick-sched.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 71f64ee..c3aed50 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -922,6 +922,22 @@ void tick_nohz_idle_exit(void) > > ts->inidle = 0; > > + /* > + * Can idle_active be false here? > + * Ideally this would be the sequence of calls: > + * - tick_nohz_idle_enter(), i.e. idle_active = true; > + * - local_irq_disable() > + * - IDLE > + * - wake up due to IPI or other interrupt > + * - local_irq_enable() > + * - tick_nohz_irq_enter(), i.e. idle_active = false; > + * - tick_nohz_irq_exit(), i.e. idle_active = true; This is not called > + * in case of IPI's as need_resched() will prevent that in > + * tick_irq_exit(), as we don't need to account any more for idle time > + * or try to enter dyntics mode (We are going to exit idle state). > + * > + * - tick_nohz_idle_exit() > + */ > if (ts->idle_active || ts->tick_stopped) > now = ktime_get();
It's still over-detailed. Much of the above is easily deduced after common review. OTOH I proposed to summarize there: https://lkml.org/lkml/2014/4/11/334 The below disambiguates it a bit further. Now it's eventually getting as big as your comment ;-) /* * ts->idle_active drives the idle time which typically elapses in the idle loop * but breaks on IRQs interrupting idle loop. * * Hence ts->idle_active can be 1 here if we exit the idle loop without the help of * an IRQ. OTOH it can be 0 on idle exit if a wake up IPI pulled the CPU out of * the idle loop. Since we know that we'll be exiting the idle task after the wake * up IPI, all the pending idle sleep time is flushed on irq entry and no more is * accounted further thanks to the need_resched() check on irq_exit(). */ Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
