Commit d02c0711 authored Mar 23, 2016 by Srikar Dronamraju Committed by Ingo Molnar Mar 31, 2016

sched/fair: Reset nr_balance_failed after active balancing



To force a task migration during active balancing, nr_balance_failed is set
to cache_nice_tries + 1. However nr_balance_failed is not reset. As a side
effect, the next regular load balance under the same sd, a cache hot task
might be migrated, just because nr_balance_failed count is high.

Resetting nr_balance_failed after a successful active balance ensures
that a hot task is not unreasonably migrated. This can be verified by
looking at othe number of hot task migrations reported by /proc/schedstat.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1458735884-30105-1-git-send-email-srikar@linux.vnet.ibm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent d740037f

kernel/sched/fair.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -7399,10 +7399,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
		&busiest->active_balance_work);
		}

		/*
		* We've kicked active balancing, reset the failure
		* counter.
		*/
		/* We've kicked active balancing, force task migration. */
		sd->nr_balance_failed = sd->cache_nice_tries+1;
		}
		} else
		@@ -7637,11 +7634,14 @@ static int active_load_balance_cpu_stop(void *data)
		schedstat_inc(sd, alb_count);

		p = detach_one_task(&env);
		if (p)
		if (p) {
		schedstat_inc(sd, alb_pushed);
		else
		/* Active balancing done, reset the failure counter. */
		sd->nr_balance_failed = 0;
		} else {
		schedstat_inc(sd, alb_failed);
		}
		}
		rcu_read_unlock();
		out_unlock:
		busiest_rq->active_balance = 0;