Commit 36c6e17b authored by Valentin Schneider's avatar Valentin Schneider Committed by Peter Zijlstra
Browse files

sched/core: Print out straggler tasks in sched_cpu_dying() 



Since commit

  1cf12e08 ("sched/hotplug: Consolidate task migration on CPU unplug")

tasks are expected to move themselves out of a out-going CPU. For most
tasks this will be done automagically via BALANCE_PUSH, but percpu kthreads
will have to cooperate and move themselves away one way or another.

Currently, some percpu kthreads (workqueues being a notable exemple) do not
cooperate nicely and can end up on an out-going CPU at the time
sched_cpu_dying() is invoked.

Print the dying rq's tasks to shed some light on the stragglers.

Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Tested-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210113183141.11974-1-valentin.schneider@arm.com
parent 9c7d9017

kernel/sched/core.c

+23 −1
Original line number Diff line number Diff line
@@ -7574,6 +7574,25 @@ static void calc_load_migrate(struct rq *rq) 
		atomic_long_add(delta, &calc_load_tasks);

}



static void dump_rq_tasks(struct rq *rq, const char *loglvl)

{

	struct task_struct *g, *p;

	int cpu = cpu_of(rq);



	lockdep_assert_held(&rq->lock);



	printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running);

	for_each_process_thread(g, p) {

		if (task_cpu(p) != cpu)

			continue;



		if (!task_on_rq_queued(p))

			continue;



		printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);

	}

}



int sched_cpu_dying(unsigned int cpu)

{

	struct rq *rq = cpu_rq(cpu);
@@ -7583,7 +7602,10 @@ int sched_cpu_dying(unsigned int cpu) 
	sched_tick_stop(cpu);



	rq_lock_irqsave(rq, &rf);

	BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq));

	if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) {

		WARN(true, "Dying CPU not properly vacated!");

		dump_rq_tasks(rq, KERN_WARNING);

	}

	rq_unlock_irqrestore(rq, &rf);



	calc_load_migrate(rq);