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Subject[RFC PATCH 5/6] sched/fair: trigger the update of blocked load on newly idle cpu
Date
Instead of waking up a random and already idle CPU, we can take advantage
of this_cpu being about to enter idle to run the ILB and update the
blocked load.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
include/linux/sched/nohz.h | 2 ++
kernel/sched/fair.c | 11 ++++++++---
kernel/sched/idle.c | 6 ++++++
3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched/nohz.h b/include/linux/sched/nohz.h
index 6d67e9a5af6b..74cdc4e87310 100644
--- a/include/linux/sched/nohz.h
+++ b/include/linux/sched/nohz.h
@@ -9,8 +9,10 @@
#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
extern void nohz_balance_enter_idle(int cpu);
extern int get_nohz_timer_target(void);
+extern void nohz_run_idle_balance(int cpu);
#else
static inline void nohz_balance_enter_idle(int cpu) { }
+static inline void nohz_run_idle_balance(int cpu) { }
#endif

#ifdef CONFIG_NO_HZ_COMMON
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 935594cd5430..3d2ab28d5736 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10461,6 +10461,11 @@ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
return true;
}

+void nohz_run_idle_balance(int cpu)
+{
+ nohz_idle_balance(cpu_rq(cpu), CPU_IDLE);
+}
+
static void nohz_newidle_balance(struct rq *this_rq)
{
int this_cpu = this_rq->cpu;
@@ -10482,10 +10487,10 @@ static void nohz_newidle_balance(struct rq *this_rq)
return;

/*
- * Blocked load of idle CPUs need to be updated.
- * Kick an ILB to update statistics.
+ * Set the need to trigger ILB in order to update blocked load
+ * before entering idle state.
*/
- kick_ilb(NOHZ_STATS_KICK);
+ this_rq->nohz_idle_balance = NOHZ_STATS_KICK;
}

#else /* !CONFIG_NO_HZ_COMMON */
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 305727ea0677..52a4e9ce2f9b 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -261,6 +261,12 @@ static void cpuidle_idle_call(void)
static void do_idle(void)
{
int cpu = smp_processor_id();
+
+ /*
+ * Check if we need to update some blocked load
+ */
+ nohz_run_idle_balance(cpu);
+
/*
* If the arch has a polling bit, we maintain an invariant:
*
--
2.17.1
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