diff options
| -rw-r--r-- | kernel/workqueue.c | 141 |
1 files changed, 42 insertions, 99 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 31d8a4586d4c..770c1a8128bf 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -126,7 +126,6 @@ enum { struct global_cwq; struct worker_pool; -struct idle_rebind; /* * The poor guys doing the actual heavy lifting. All on-duty workers @@ -150,7 +149,6 @@ struct worker { int id; /* I: worker id */ /* for rebinding worker to CPU */ - struct idle_rebind *idle_rebind; /* L: for idle worker */ struct work_struct rebind_work; /* L: for busy worker */ }; @@ -160,6 +158,8 @@ struct worker_pool { struct list_head worklist; /* L: list of pending works */ int nr_workers; /* L: total number of workers */ + + /* nr_idle includes the ones off idle_list for rebinding */ int nr_idle; /* L: currently idle ones */ struct list_head idle_list; /* X: list of idle workers */ @@ -186,8 +186,6 @@ struct global_cwq { struct worker_pool pools[NR_WORKER_POOLS]; /* normal and highpri pools */ - - wait_queue_head_t rebind_hold; /* rebind hold wait */ } ____cacheline_aligned_in_smp; /* @@ -687,6 +685,13 @@ static bool too_many_workers(struct worker_pool *pool) int nr_idle = pool->nr_idle + managing; /* manager is considered idle */ int nr_busy = pool->nr_workers - nr_idle; + /* + * nr_idle and idle_list may disagree if idle rebinding is in + * progress. Never return %true if idle_list is empty. + */ + if (list_empty(&pool->idle_list)) + return false; + return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy; } @@ -1611,37 +1616,26 @@ __acquires(&gcwq->lock) } } -struct idle_rebind { - int cnt; /* # workers to be rebound */ - struct completion done; /* all workers rebound */ -}; - /* - * Rebind an idle @worker to its CPU. During CPU onlining, this has to - * happen synchronously for idle workers. worker_thread() will test + * Rebind an idle @worker to its CPU. worker_thread() will test * %WORKER_REBIND before leaving idle and call this function. */ static void idle_worker_rebind(struct worker *worker) { struct global_cwq *gcwq = worker->pool->gcwq; - /* CPU must be online at this point */ - WARN_ON(!worker_maybe_bind_and_lock(worker)); - if (!--worker->idle_rebind->cnt) - complete(&worker->idle_rebind->done); - spin_unlock_irq(&worker->pool->gcwq->lock); - - /* we did our part, wait for rebind_workers() to finish up */ - wait_event(gcwq->rebind_hold, !(worker->flags & WORKER_REBIND)); - /* - * rebind_workers() shouldn't finish until all workers passed the - * above WORKER_REBIND wait. Tell it when done. + * CPU may go down again inbetween. If rebinding fails, reinstate + * UNBOUND. We're off idle_list and nobody else can do it for us. */ - spin_lock_irq(&worker->pool->gcwq->lock); - if (!--worker->idle_rebind->cnt) - complete(&worker->idle_rebind->done); - spin_unlock_irq(&worker->pool->gcwq->lock); + if (!worker_maybe_bind_and_lock(worker)) + worker->flags |= WORKER_UNBOUND; + + worker_clr_flags(worker, WORKER_REBIND); + + /* rebind complete, become available again */ + list_add(&worker->entry, &worker->pool->idle_list); + spin_unlock_irq(&gcwq->lock); } /* @@ -1676,29 +1670,25 @@ static void busy_worker_rebind_fn(struct work_struct *work) * @gcwq->cpu is coming online. Rebind all workers to the CPU. Rebinding * is different for idle and busy ones. * - * The idle ones should be rebound synchronously and idle rebinding should - * be complete before any worker starts executing work items with - * concurrency management enabled; otherwise, scheduler may oops trying to - * wake up non-local idle worker from wq_worker_sleeping(). - * - * This is achieved by repeatedly requesting rebinding until all idle - * workers are known to have been rebound under @gcwq->lock and holding all - * idle workers from becoming busy until idle rebinding is complete. + * Idle ones will be removed from the idle_list and woken up. They will + * add themselves back after completing rebind. This ensures that the + * idle_list doesn't contain any unbound workers when re-bound busy workers + * try to perform local wake-ups for concurrency management. * - * Once idle workers are rebound, busy workers can be rebound as they - * finish executing their current work items. Queueing the rebind work at - * the head of their scheduled lists is enough. Note that nr_running will - * be properbly bumped as busy workers rebind. + * Busy workers can rebind after they finish their current work items. + * Queueing the rebind work item at the head of the scheduled list is + * enough. Note that nr_running will be properly bumped as busy workers + * rebind. * - * On return, all workers are guaranteed to either be bound or have rebind - * work item scheduled. + * On return, all non-manager workers are scheduled for rebind - see + * manage_workers() for the manager special case. Any idle worker + * including the manager will not appear on @idle_list until rebind is + * complete, making local wake-ups safe. */ static void rebind_workers(struct global_cwq *gcwq) - __releases(&gcwq->lock) __acquires(&gcwq->lock) { - struct idle_rebind idle_rebind; struct worker_pool *pool; - struct worker *worker; + struct worker *worker, *n; struct hlist_node *pos; int i; @@ -1707,46 +1697,29 @@ static void rebind_workers(struct global_cwq *gcwq) for_each_worker_pool(pool, gcwq) lockdep_assert_held(&pool->manager_mutex); - /* - * Rebind idle workers. Interlocked both ways. We wait for - * workers to rebind via @idle_rebind.done. Workers will wait for - * us to finish up by watching %WORKER_REBIND. - */ - init_completion(&idle_rebind.done); -retry: - idle_rebind.cnt = 1; - INIT_COMPLETION(idle_rebind.done); - - /* set REBIND and kick idle ones, we'll wait for these later */ + /* set REBIND and kick idle ones */ for_each_worker_pool(pool, gcwq) { - list_for_each_entry(worker, &pool->idle_list, entry) { + list_for_each_entry_safe(worker, n, &pool->idle_list, entry) { unsigned long worker_flags = worker->flags; - if (worker->flags & WORKER_REBIND) - continue; - /* morph UNBOUND to REBIND atomically */ worker_flags &= ~WORKER_UNBOUND; worker_flags |= WORKER_REBIND; ACCESS_ONCE(worker->flags) = worker_flags; - idle_rebind.cnt++; - worker->idle_rebind = &idle_rebind; + /* + * idle workers should be off @pool->idle_list + * until rebind is complete to avoid receiving + * premature local wake-ups. + */ + list_del_init(&worker->entry); /* worker_thread() will call idle_worker_rebind() */ wake_up_process(worker->task); } } - if (--idle_rebind.cnt) { - spin_unlock_irq(&gcwq->lock); - wait_for_completion(&idle_rebind.done); - spin_lock_irq(&gcwq->lock); - /* busy ones might have become idle while waiting, retry */ - goto retry; - } - - /* all idle workers are rebound, rebind busy workers */ + /* rebind busy workers */ for_each_busy_worker(worker, i, pos, gcwq) { unsigned long worker_flags = worker->flags; struct work_struct *rebind_work = &worker->rebind_work; @@ -1776,34 +1749,6 @@ retry: worker->scheduled.next, work_color_to_flags(WORK_NO_COLOR)); } - - /* - * All idle workers are rebound and waiting for %WORKER_REBIND to - * be cleared inside idle_worker_rebind(). Clear and release. - * Clearing %WORKER_REBIND from this foreign context is safe - * because these workers are still guaranteed to be idle. - * - * We need to make sure all idle workers passed WORKER_REBIND wait - * in idle_worker_rebind() before returning; otherwise, workers can - * get stuck at the wait if hotplug cycle repeats. - */ - idle_rebind.cnt = 1; - INIT_COMPLETION(idle_rebind.done); - - for_each_worker_pool(pool, gcwq) { - list_for_each_entry(worker, &pool->idle_list, entry) { - worker->flags &= ~WORKER_REBIND; - idle_rebind.cnt++; - } - } - - wake_up_all(&gcwq->rebind_hold); - - if (--idle_rebind.cnt) { - spin_unlock_irq(&gcwq->lock); - wait_for_completion(&idle_rebind.done); - spin_lock_irq(&gcwq->lock); - } } static struct worker *alloc_worker(void) @@ -3916,8 +3861,6 @@ static int __init init_workqueues(void) mutex_init(&pool->manager_mutex); ida_init(&pool->worker_ida); } - - init_waitqueue_head(&gcwq->rebind_hold); } /* create the initial worker */ |