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Date: Wed, 16 Jul 2014 09:28:55 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: Lai Jiangshan <laijs@...fujitsu.com>
CC: <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 1/1 V2] workqueue: unfold start_worker() into create_worker()
On 07/14/2014 12:05 PM, Lai Jiangshan wrote:
> Simply unfold the code of start_worker() into create_worker() and
> remove the original start_worker() and create_and_start_worker().
>
> The only trade-off is the introduced overhead that the pool->lock
> is released and re-grabbed after the newly worker is started.
> The overhead is acceptable since the manager is slow path.
Hi, TJ
Will you accept this trade-off and the patch?
If so, I will rebase this patch without any dependence on other patch.
Thanks,
Lai
>
> And because this new locking behavior, the newly created worker
> may grab the lock earlier than the manager and go to process
> work items. In this case, the need_to_create_worker() may be
> true as expected and the manager goes to restart without complaint.
>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> kernel/workqueue.c | 69 ++++++++++------------------------------------------
> 1 files changed, 13 insertions(+), 56 deletions(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 2b3c12c..5b68527 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1553,7 +1553,7 @@ static void worker_enter_idle(struct worker *worker)
> (worker->hentry.next || worker->hentry.pprev)))
> return;
>
> - /* can't use worker_set_flags(), also called from start_worker() */
> + /* can't use worker_set_flags(), also called from create_worker() */
> worker->flags |= WORKER_IDLE;
> pool->nr_idle++;
> worker->last_active = jiffies;
> @@ -1674,8 +1674,7 @@ static void worker_detach_from_pool(struct worker *worker,
> * create_worker - create a new workqueue worker
> * @pool: pool the new worker will belong to
> *
> - * Create a new worker which is attached to @pool. The new worker must be
> - * started by start_worker().
> + * Create and start a new worker which is attached to @pool.
> *
> * CONTEXT:
> * Might sleep. Does GFP_KERNEL allocations.
> @@ -1720,6 +1719,13 @@ static struct worker *create_worker(struct worker_pool *pool)
> /* successful, attach the worker to the pool */
> worker_attach_to_pool(worker, pool);
>
> + /* start the newly created worker */
> + spin_lock_irq(&pool->lock);
> + worker->pool->nr_workers++;
> + worker_enter_idle(worker);
> + wake_up_process(worker->task);
> + spin_unlock_irq(&pool->lock);
> +
> return worker;
>
> fail:
> @@ -1730,44 +1736,6 @@ fail:
> }
>
> /**
> - * start_worker - start a newly created worker
> - * @worker: worker to start
> - *
> - * Make the pool aware of @worker and start it.
> - *
> - * CONTEXT:
> - * spin_lock_irq(pool->lock).
> - */
> -static void start_worker(struct worker *worker)
> -{
> - worker->pool->nr_workers++;
> - worker_enter_idle(worker);
> - wake_up_process(worker->task);
> -}
> -
> -/**
> - * create_and_start_worker - create and start a worker for a pool
> - * @pool: the target pool
> - *
> - * Grab the managership of @pool and create and start a new worker for it.
> - *
> - * Return: 0 on success. A negative error code otherwise.
> - */
> -static int create_and_start_worker(struct worker_pool *pool)
> -{
> - struct worker *worker;
> -
> - worker = create_worker(pool);
> - if (worker) {
> - spin_lock_irq(&pool->lock);
> - start_worker(worker);
> - spin_unlock_irq(&pool->lock);
> - }
> -
> - return worker ? 0 : -ENOMEM;
> -}
> -
> -/**
> * destroy_worker - destroy a workqueue worker
> * @worker: worker to be destroyed
> *
> @@ -1905,18 +1873,7 @@ restart:
> mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
>
> while (true) {
> - struct worker *worker;
> -
> - worker = create_worker(pool);
> - if (worker) {
> - spin_lock_irq(&pool->lock);
> - start_worker(worker);
> - if (WARN_ON_ONCE(need_to_create_worker(pool)))
> - goto restart;
> - return true;
> - }
> -
> - if (!need_to_create_worker(pool))
> + if (create_worker(pool) || !need_to_create_worker(pool))
> break;
>
> schedule_timeout_interruptible(CREATE_COOLDOWN);
> @@ -3543,7 +3500,7 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
> goto fail;
>
> /* create and start the initial worker */
> - if (create_and_start_worker(pool) < 0)
> + if (!create_worker(pool))
> goto fail;
>
> /* install */
> @@ -4617,7 +4574,7 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
> for_each_cpu_worker_pool(pool, cpu) {
> if (pool->nr_workers)
> continue;
> - if (create_and_start_worker(pool) < 0)
> + if (!create_worker(pool))
> return NOTIFY_BAD;
> }
> break;
> @@ -4917,7 +4874,7 @@ static int __init init_workqueues(void)
>
> for_each_cpu_worker_pool(pool, cpu) {
> pool->flags &= ~POOL_DISASSOCIATED;
> - BUG_ON(create_and_start_worker(pool) < 0);
> + BUG_ON(!create_worker(pool));
> }
> }
>
--
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