diff mbox series

[5.8,012/464] sched/fair: Fix NOHZ next idle balance

Message ID 20200817143834.344555529@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman Aug. 17, 2020, 3:09 p.m. UTC 
From: Vincent Guittot <vincent.guittot@linaro.org>


[ Upstream commit 3ea2f097b17e13a8280f1f9386c331b326a3dbef ]

With commit:
  'b7031a02ec75 ("sched/fair: Add NOHZ_STATS_KICK")'
rebalance_domains of the local cfs_rq happens before others idle cpus have
updated nohz.next_balance and its value is overwritten.

Move the update of nohz.next_balance for other idles cpus before balancing
and updating the next_balance of local cfs_rq.

Also, the nohz.next_balance is now updated only if all idle cpus got a
chance to rebalance their domains and the idle balance has not been aborted
because of new activities on the CPU. In case of need_resched, the idle
load balance will be kick the next jiffie in order to address remaining
ilb.

Fixes: b7031a02ec75 ("sched/fair: Add NOHZ_STATS_KICK")
Reported-by: Peng Liu <iwtbavbm@gmail.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

Acked-by: Mel Gorman <mgorman@suse.de>

Link: https://lkml.kernel.org/r/20200609123748.18636-1-vincent.guittot@linaro.org
Signed-off-by: Sasha Levin <sashal@kernel.org>

---
 kernel/sched/fair.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

-- 
2.25.1
diff mbox series

Patch

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 04fa8dbcfa4d7..6b3b59cc51d6c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10027,7 +10027,12 @@  static void kick_ilb(unsigned int flags)
 {
 	int ilb_cpu;
 
-	nohz.next_balance++;
+	/*
+	 * Increase nohz.next_balance only when if full ilb is triggered but
+	 * not if we only update stats.
+	 */
+	if (flags & NOHZ_BALANCE_KICK)
+		nohz.next_balance = jiffies+1;
 
 	ilb_cpu = find_new_ilb();
 
@@ -10348,6 +10353,14 @@  static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
 		}
 	}
 
+	/*
+	 * next_balance will be updated only when there is a need.
+	 * When the CPU is attached to null domain for ex, it will not be
+	 * updated.
+	 */
+	if (likely(update_next_balance))
+		nohz.next_balance = next_balance;
+
 	/* Newly idle CPU doesn't need an update */
 	if (idle != CPU_NEWLY_IDLE) {
 		update_blocked_averages(this_cpu);
@@ -10368,14 +10381,6 @@  static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
 	if (has_blocked_load)
 		WRITE_ONCE(nohz.has_blocked, 1);
 
-	/*
-	 * next_balance will be updated only when there is a need.
-	 * When the CPU is attached to null domain for ex, it will not be
-	 * updated.
-	 */
-	if (likely(update_next_balance))
-		nohz.next_balance = next_balance;
-
 	return ret;
 }