From: Vincent Guittot <vincent.guittot@linaro.org>
To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
dietmar.eggemann@arm.com, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de,
linux-kernel@vger.kernel.org, iwtbavbm@gmail.com
Cc: valentin.schneider@arm.com, Vincent Guittot <vincent.guittot@linaro.org>
Subject: [PATCH v2] sched/fair: fix nohz next idle balance
Date: Tue, 9 Jun 2020 14:37:48 +0200 [thread overview]
Message-ID: <20200609123748.18636-1-vincent.guittot@linaro.org> (raw)
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.
Reported-by: Peng Liu <iwtbavbm@gmail.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
- Changes v2:
- use jiffies instead of incrementing nohz.next_balance to be sure of the
value. The change slipped out of the previous version.
kernel/sched/fair.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0ed04d2a8959..832164d441dd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10017,7 +10017,12 @@ 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();
@@ -10338,6 +10343,14 @@ 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);
@@ -10358,14 +10371,6 @@ 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;
}
--
2.17.1
next reply other threads:[~2020-06-09 12:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-09 12:37 Vincent Guittot [this message]
2020-06-10 12:49 ` [PATCH v2] sched/fair: fix nohz next idle balance Peter Zijlstra
2020-06-11 14:12 ` Valentin Schneider
2020-06-11 14:28 ` Peter Zijlstra
2020-06-11 14:43 ` Mel Gorman
2020-06-16 12:21 ` [tip: sched/core] sched/fair: Fix NOHZ " tip-bot2 for Vincent Guittot
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