On Tuesday 22 April 2014 04:50 AM, Frederic Weisbecker wrote:
> 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.
Hmm.. Something broke for sure in my repo. I do remember updating this patch
with your
comments and something went wrong while playing with patches.
Sorry for that. Fixed my repo now.
> 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().
> */
@Thomas: Please consider this patch instead:
Author: Viresh Kumar <viresh.ku...@linaro.org>
Date: Mon Apr 21 15:25:10 2014 +0530
tick-sched: add comment about 'idle_active' in tick_nohz_idle_exit()
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 | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 71f64ee..b2f024f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -922,6 +922,17 @@ void tick_nohz_idle_exit(void)
ts->inidle = 0;
+ /*
+ * 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().
+ */
if (ts->idle_active || ts->tick_stopped)
now = ktime_get();
--
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