sched: Reset loop counters if all tasks are pinned and we need to redo load balance

Prashanth Nageshappa · Ingo Molnar · commit bbf18b194959 · 2012-07-24T13:55:37.000+02:00
While load balancing, if all tasks on the source runqueue are pinned, we retry after excluding the corresponding source cpu. However, loop counters env.loop and env.loop_break are not reset before retrying, which can lead to failure in moving the tasks. In this patch we reset env.loop and env.loop_break to their inital values before we retry. Signed-off-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/4FE06EEF.2090709@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
@@ -4288,8 +4288,11 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 		/* All tasks on this runqueue were pinned by CPU affinity */
 		if (unlikely(env.flags & LBF_ALL_PINNED)) {
 			cpumask_clear_cpu(cpu_of(busiest), cpus);
-			if (!cpumask_empty(cpus))
+			if (!cpumask_empty(cpus)) {
+				env.loop = 0;
+				env.loop_break = sched_nr_migrate_break;
 				goto redo;
+			}
 			goto out_balanced;
 		}
 	}

Original file line number	Diff line number	Diff line change
`@@ -4288,8 +4288,11 @@ static int load_balance(int this_cpu, struct rq *this_rq,`
`4288`	`4288`	`/* All tasks on this runqueue were pinned by CPU affinity */`
`4289`	`4289`	`if (unlikely(env.flags & LBF_ALL_PINNED)) {`
`4290`	`4290`	`cpumask_clear_cpu(cpu_of(busiest), cpus);`
`4291`		`- if (!cpumask_empty(cpus))`
	`4291`	`+ if (!cpumask_empty(cpus)) {`
	`4292`	`+ env.loop = 0;`
	`4293`	`+ env.loop_break = sched_nr_migrate_break;`
`4292`	`4294`	`goto redo;`
	`4295`	`+ }`
`4293`	`4296`	`goto out_balanced;`
`4294`	`4297`	`}`
`4295`	`4298`	`}`