Commit 3ea2f097 authored Jun 09, 2020 by Vincent Guittot Committed by Peter Zijlstra Jun 15, 2020

sched/fair: Fix NOHZ next idle balance



With commit:
  'b7031a02 ("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: b7031a02 ("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

parent b4098bfc

kernel/sched/fair.c

+14 −9

Original line number	Diff line number	Diff line
		@@ -10022,7 +10022,12 @@ 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();

		@@ -10343,6 +10348,14 @@ 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);
		@@ -10363,14 +10376,6 @@ abort:
		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;
		}

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