After we introduce multiple pools for cpu pools, a part of the comments in wq_unbind_fn() becomes wrong.
It said that "current worker would trigger unbound chain execution". It is wrong. current worker only belongs to one of the multiple pools. If wq_unbind_fn() does unbind the normal_pri pool(not the pool of the current worker), the current worker is not the available worker to trigger unbound chain execution of the normal_pri pool, and if all the workers of the normal_pri goto sleep after they were set %WORKER_UNBOUND but before they finish their current work, unbound chain execution is not triggered totally. The pool is stopped! We can change wq_unbind_fn() only does unbind one pool and we launch multiple wq_unbind_fn()s, one for each pool to solve the problem. But this change will add much latency to hotplug path unnecessarily. So we choice to wake up a worker directly to trigger unbound chain execution. current worker may sleep on &second_pool->assoc_mutex, so we also move the wakeup code into the loop to avoid second_pool silences the first_pool. Signed-off-by: Lai Jiangshan <[email protected]> --- kernel/workqueue.c | 45 ++++++++++++++++++++++++++------------------- 1 files changed, 26 insertions(+), 19 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 81f2457..03159c2 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3446,28 +3446,35 @@ static void wq_unbind_fn(struct work_struct *work) spin_unlock_irq(&pool->lock); mutex_unlock(&pool->assoc_mutex); - } - /* - * Call schedule() so that we cross rq->lock and thus can guarantee - * sched callbacks see the %WORKER_UNBOUND flag. This is necessary - * as scheduler callbacks may be invoked from other cpus. - */ - schedule(); + /* + * Call schedule() so that we cross rq->lock and thus can + * guarantee sched callbacks see the %WORKER_UNBOUND flag. + * This is necessary as scheduler callbacks may be invoked + * from other cpus. + */ + schedule(); - /* - * Sched callbacks are disabled now. Zap nr_running. After this, - * nr_running stays zero and need_more_worker() and keep_working() - * are always true as long as the worklist is not empty. Pools on - * @cpu now behave as unbound (in terms of concurrency management) - * pools which are served by workers tied to the CPU. - * - * On return from this function, the current worker would trigger - * unbound chain execution of pending work items if other workers - * didn't already. - */ - for_each_std_worker_pool(pool, cpu) + /* + * Sched callbacks are disabled now. Zap nr_running. + * After this, nr_running stays zero and need_more_worker() + * and keep_working() are always true as long as the worklist + * is not empty. This pool now behave as unbound (in terms of + * concurrency management) pool which are served by workers + * tied to the pool. + */ atomic_set(&pool->nr_running, 0); + + /* The current busy workers of this pool may goto sleep without + * wake up any other worker after they were set %WORKER_UNBOUND + * flag. Here we wake up another possible worker to start + * the unbound chain execution of pending work items in this + * case. + */ + spin_lock_irq(&pool->lock); + wake_up_worker(pool); + spin_unlock_irq(&pool->lock); + } } /* -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
