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Commit bc2ae0f5 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: drop @bind from create_worker() 



Currently, create_worker()'s callers are responsible for deciding
whether the newly created worker should be bound to the associated CPU
and create_worker() sets WORKER_UNBOUND only for the workers for the
unbound global_cwq.  Creation during normal operation is always via
maybe_create_worker() and @bind is true.  For workers created during
hotplug, @bind is false.

Normal operation path is planned to be used even while the CPU is
going through hotplug operations or offline and this static decision
won't work.

Drop @bind from create_worker() and decide whether to bind by looking
at GCWQ_DISASSOCIATED.  create_worker() will also set WORKER_UNBOUND
autmatically if disassociated.  To avoid flipping GCWQ_DISASSOCIATED
while create_worker() is in progress, the flag is now allowed to be
changed only while holding all manager_mutexes on the global_cwq.

This requires that GCWQ_DISASSOCIATED is not cleared behind trustee's
back.  CPU_ONLINE no longer clears DISASSOCIATED before flushing
trustee, which clears DISASSOCIATED before rebinding remaining workers
if asked to release.  For cases where trustee isn't around, CPU_ONLINE
clears DISASSOCIATED after flushing trustee.  Also, now, first_idle
has UNBOUND set on creation which is explicitly cleared by CPU_ONLINE
while binding it.  These convolutions will soon be removed by further
simplification of CPU hotplug path.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatar"Rafael J. Wysocki" <rjw@sisk.pl>
parent 60373152

kernel/workqueue.c

+45 −19
Original line number Diff line number Diff line
@@ -45,7 +45,22 @@ 
#include "workqueue_sched.h"



enum {

	/* global_cwq flags */

	/*

	 * global_cwq flags

	 *

	 * A bound gcwq is either associated or disassociated with its CPU.

	 * While associated (!DISASSOCIATED), all workers are bound to the

	 * CPU and none has %WORKER_UNBOUND set and concurrency management

	 * is in effect.

	 *

	 * While DISASSOCIATED, the cpu may be offline and all workers have

	 * %WORKER_UNBOUND set and concurrency management disabled, and may

	 * be executing on any CPU.  The gcwq behaves as an unbound one.

	 *

	 * Note that DISASSOCIATED can be flipped only while holding

	 * managership of all pools on the gcwq to avoid changing binding

	 * state while create_worker() is in progress.

	 */

	GCWQ_DISASSOCIATED	= 1 << 0,	/* cpu can't serve workers */

	GCWQ_FREEZING		= 1 << 1,	/* freeze in progress */
@@ -1334,7 +1349,6 @@ static struct worker *alloc_worker(void) 
/**

 * create_worker - create a new workqueue worker

 * @pool: pool the new worker will belong to

 * @bind: whether to set affinity to @cpu or not

 *

 * Create a new worker which is bound to @pool.  The returned worker

 * can be started by calling start_worker() or destroyed using
@@ -1346,10 +1360,9 @@ static struct worker *alloc_worker(void) 
 * RETURNS:

 * Pointer to the newly created worker.

 */

static struct worker *create_worker(struct worker_pool *pool, bool bind)

static struct worker *create_worker(struct worker_pool *pool)

{

	struct global_cwq *gcwq = pool->gcwq;

	bool on_unbound_cpu = gcwq->cpu == WORK_CPU_UNBOUND;

	const char *pri = worker_pool_pri(pool) ? "H" : "";

	struct worker *worker = NULL;

	int id = -1;
@@ -1370,7 +1383,7 @@ static struct worker *create_worker(struct worker_pool *pool, bool bind) 
	worker->pool = pool;

	worker->id = id;



	if (!on_unbound_cpu)

	if (gcwq->cpu != WORK_CPU_UNBOUND)

		worker->task = kthread_create_on_node(worker_thread,

					worker, cpu_to_node(gcwq->cpu),

					"kworker/%u:%d%s", gcwq->cpu, id, pri);
@@ -1384,14 +1397,18 @@ static struct worker *create_worker(struct worker_pool *pool, bool bind) 
		set_user_nice(worker->task, HIGHPRI_NICE_LEVEL);



	/*

	 * An unbound worker will become a regular one if CPU comes online

	 * later on.  Make sure every worker has PF_THREAD_BOUND set.

	 * Determine CPU binding of the new worker depending on

	 * %GCWQ_DISASSOCIATED.  The caller is responsible for ensuring the

	 * flag remains stable across this function.  See the comments

	 * above the flag definition for details.

	 *

	 * As an unbound worker may later become a regular one if CPU comes

	 * online, make sure every worker has %PF_THREAD_BOUND set.

	 */

	if (bind && !on_unbound_cpu)

	if (!(gcwq->flags & GCWQ_DISASSOCIATED)) {

		kthread_bind(worker->task, gcwq->cpu);

	else {

	} else {

		worker->task->flags |= PF_THREAD_BOUND;

		if (on_unbound_cpu)

		worker->flags |= WORKER_UNBOUND;

	}
@@ -1568,7 +1585,7 @@ restart: 
	while (true) {

		struct worker *worker;



		worker = create_worker(pool, true);

		worker = create_worker(pool);

		if (worker) {

			del_timer_sync(&pool->mayday_timer);

			spin_lock_irq(&gcwq->lock);
@@ -3420,14 +3437,12 @@ static int __cpuinit trustee_thread(void *__gcwq) 


			if (need_to_create_worker(pool)) {

				spin_unlock_irq(&gcwq->lock);

				worker = create_worker(pool, false);

				worker = create_worker(pool);

				spin_lock_irq(&gcwq->lock);

				if (worker) {

					worker->flags |= WORKER_UNBOUND;

				if (worker)

					start_worker(worker);

			}

		}

		}



		/* give a breather */

		if (trustee_wait_event_timeout(false, TRUSTEE_COOLDOWN) < 0)
@@ -3463,6 +3478,10 @@ static int __cpuinit trustee_thread(void *__gcwq) 
	for_each_worker_pool(pool, gcwq)

		WARN_ON(!list_empty(&pool->idle_list));



	/* if we're reassociating, clear DISASSOCIATED */

	if (gcwq->trustee_state == TRUSTEE_RELEASE)

		gcwq->flags &= ~GCWQ_DISASSOCIATED;



	for_each_busy_worker(worker, i, pos, gcwq) {

		struct work_struct *rebind_work = &worker->rebind_work;
@@ -3546,7 +3565,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb, 
		i = 0;

		for_each_worker_pool(pool, gcwq) {

			BUG_ON(pool->first_idle);

			new_workers[i] = create_worker(pool, false);

			new_workers[i] = create_worker(pool);

			if (!new_workers[i++])

				goto err_destroy;

		}
@@ -3584,13 +3603,19 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb, 


	case CPU_DOWN_FAILED:

	case CPU_ONLINE:

		gcwq->flags &= ~GCWQ_DISASSOCIATED;

		if (gcwq->trustee_state != TRUSTEE_DONE) {

			gcwq->trustee_state = TRUSTEE_RELEASE;

			wake_up_process(gcwq->trustee);

			wait_trustee_state(gcwq, TRUSTEE_DONE);

		}



		/*

		 * Either DISASSOCIATED is already cleared or no worker is

		 * left on the gcwq.  Safe to clear DISASSOCIATED without

		 * claiming managers.

		 */

		gcwq->flags &= ~GCWQ_DISASSOCIATED;



		/*

		 * Trustee is done and there might be no worker left.

		 * Put the first_idle in and request a real manager to
@@ -3601,6 +3626,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb, 
			kthread_bind(pool->first_idle->task, cpu);

			spin_lock_irq(&gcwq->lock);

			pool->flags |= POOL_MANAGE_WORKERS;

			pool->first_idle->flags &= ~WORKER_UNBOUND;

			start_worker(pool->first_idle);

			pool->first_idle = NULL;

		}
@@ -3899,7 +3925,7 @@ static int __init init_workqueues(void) 
		for_each_worker_pool(pool, gcwq) {

			struct worker *worker;



			worker = create_worker(pool, true);

			worker = create_worker(pool);

			BUG_ON(!worker);

			spin_lock_irq(&gcwq->lock);

			start_worker(worker);