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Subject[PATCH 32/38] tick-sched: add comment about 'idle_active' in tick_nohz_idle_exit()
Date
The sequence of calls for dynticks CPUs was a bit confusing and so adding a
comment in tick_nohz_idle_exit() routine 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 <fweisbec@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@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 f1bc258..85a4e90 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -925,6 +925,22 @@ 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();

--
1.7.12.rc2.18.g61b472e


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