[RFC][PATCH 4/5] sched/fair: Push rq lock pin/unpin into idle_balance()

Matt Fleming
2016-05-12T19:50:07Z

Future patches will emit warnings if rq_clock() is called before
update_rq_clock() inside a rq_pin_lock()/rq_unpin_lock() pair.

Since there is only one caller of idle_balance() we can push the
unpin/repin there.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Yuyang Du <yuyang.du@intel.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
---
kernel/sched/fair.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7f776a99bde0..217e3a9d78db 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3095,7 +3095,7 @@ static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq)
return cfs_rq->avg.load_avg;
}

-static int idle_balance(struct rq *this_rq);
+static int idle_balance(struct rq *this_rq, struct rq_flags *rf);

#else /* CONFIG_SMP */

@@ -3118,7 +3118,7 @@ attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
static inline void
detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}

-static inline int idle_balance(struct rq *rq)
+static inline int idle_balance(struct rq *rq, struct rq_flags *rf)
{
return 0;
}
@@ -5701,15 +5701,8 @@ simple:
return p;

idle:
- /*
- * This is OK, because current is on_cpu, which avoids it being picked
- * for load-balance and preemption/IRQs are still disabled avoiding
- * further scheduler activity on it and we're being very careful to
- * re-start the picking loop.
- */
- rq_unpin_lock(rq, rf);
- new_tasks = idle_balance(rq);
- rq_repin_lock(rq, rf);
+ new_tasks = idle_balance(rq, rf);
+
/*
* Because idle_balance() releases (and re-acquires) rq->lock, it is
* possible for any higher priority task to appear. In that case we
@@ -7641,7 +7634,7 @@ update_next_balance(struct sched_domain *sd, int cpu_busy, unsigned long *next_b
* idle_balance is called by schedule() if this_cpu is about to become
* idle. Attempts to pull tasks from other CPUs.
*/
-static int idle_balance(struct rq *this_rq)
+static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
{
unsigned long next_balance = jiffies + HZ;
int this_cpu = this_rq->cpu;
@@ -7655,6 +7648,14 @@ static int idle_balance(struct rq *this_rq)
*/
this_rq->idle_stamp = rq_clock(this_rq);

+ /*
+ * This is OK, because current is on_cpu, which avoids it being picked
+ * for load-balance and preemption/IRQs are still disabled avoiding
+ * further scheduler activity on it and we're being very careful to
+ * re-start the picking loop.
+ */
+ rq_unpin_lock(this_rq, rf);
+
if (this_rq->avg_idle < sysctl_sched_migration_cost ||
!this_rq->rd->overload) {
rcu_read_lock();
@@ -7732,6 +7733,8 @@ out:
if (pulled_task)
this_rq->idle_stamp = 0;

+ rq_repin_lock(this_rq, rf);
+
return pulled_task;
}

--
2.7.3