Commit-ID: 873b4c65b519fd769940eb281f77848227d4e5c1
Gitweb: http://git.kernel.org/tip/873b4c65b519fd769940eb281f77848227d4e5c1
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
AuthorDate: Wed, 5 Jun 2013 10:13:11 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 19 Jun 2013 12:55:09 +0200
sched: Fix clear NOHZ_BALANCE_KICK
I have faced a sequence where the Idle Load Balance was sometime not
triggered for a while on my platform, in the following scenario:
CPU 0 and CPU 1 are running tasks and CPU 2 is idle
CPU 1 kicks the Idle Load Balance
CPU 1 selects CPU 2 as the new Idle Load Balancer
CPU 2 sets NOHZ_BALANCE_KICK for CPU 2
CPU 2 sends a reschedule IPI to CPU 2
While CPU 3 wakes up, CPU 0 or CPU 1 migrates a waking up task A on CPU 2
CPU 2 finally wakes up, runs task A and discards the Idle Load Balance
task A quickly goes back to sleep (before a tick occurs on CPU 2)
CPU 2 goes back to idle with NOHZ_BALANCE_KICK set
Whenever CPU 2 will be selected as the ILB, no reschedule IPI will be sent
because NOHZ_BALANCE_KICK is already set and no Idle Load Balance will be
performed.
We must wait for the sched softirq to be raised on CPU 2 thanks to another
part the kernel to come back to clear NOHZ_BALANCE_KICK.
The proposed solution clears NOHZ_BALANCE_KICK in schedule_ipi if
we can't raise the sched_softirq for the Idle Load Balance.
Change since V1:
- move the clear of NOHZ_BALANCE_KICK in got_nohz_idle_kick if the ILB
can't run on this CPU (as suggested by Peter)
Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1370419991-13870-1-git-send-email-vincent.guittot@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/core.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 58453b8..919bee6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -633,7 +633,19 @@ void wake_up_nohz_cpu(int cpu)
static inline bool got_nohz_idle_kick(void)
{
int cpu = smp_processor_id();
- return idle_cpu(cpu) && test_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu));
+
+ if (!test_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu)))
+ return false;
+
+ if (idle_cpu(cpu) && !need_resched())
+ return true;
+
+ /*
+ * We can't run Idle Load Balance on this CPU for this time so we
+ * cancel it and clear NOHZ_BALANCE_KICK
+ */
+ clear_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu));
+ return false;
}
#else /* CONFIG_NO_HZ_COMMON */
@@ -1393,8 +1405,9 @@ static void sched_ttwu_pending(void)
void scheduler_ipi(void)
{
- if (llist_empty(&this_rq()->wake_list) && !got_nohz_idle_kick()
- && !tick_nohz_full_cpu(smp_processor_id()))
+ if (llist_empty(&this_rq()->wake_list)
+ && !tick_nohz_full_cpu(smp_processor_id())
+ && !got_nohz_idle_kick())
return;
/*
@@ -1417,7 +1430,7 @@ void scheduler_ipi(void)
/*
* Check if someone kicked us for doing the nohz idle load balance.
*/
- if (unlikely(got_nohz_idle_kick() && !need_resched())) {
+ if (unlikely(got_nohz_idle_kick())) {
this_rq()->idle_balance = 1;
raise_softirq_irqoff(SCHED_SOFTIRQ);
}
--
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