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SubjectRe: [PATCH 2/2 wq/for-3.9] workqueue: reimplement is_chained_work() using current_wq_worker()
Hi, tj

Thank you for adding this one.

Would you deffer "workqueue: rename cpu_workqueue to pool_workqueue" a
little? I don't want to rebase my almost-ready work again(not a good
reason... but please...)

I will answer your other emails soon and sent the patches.

Thanks,
Lai

On 14/02/13 11:27, Tejun Heo wrote:
> is_chained_work() was added before current_wq_worker() and implemented
> its own ham-fisted way of finding out whether %current is a workqueue
> worker - it iterates through all possible workers.
>
> Drop the custom implementation and reimplement using
> current_wq_worker().
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> ---
> kernel/workqueue.c | 33 ++++++++-------------------------
> 1 file changed, 8 insertions(+), 25 deletions(-)
>
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1159,35 +1159,18 @@ static void insert_work(struct cpu_workq
>
> /*
> * Test whether @work is being queued from another work executing on the
> - * same workqueue. This is rather expensive and should only be used from
> - * cold paths.
> + * same workqueue.
> */
> static bool is_chained_work(struct workqueue_struct *wq)
> {
> - unsigned long flags;
> - unsigned int cpu;
> + struct worker *worker;
>
> - for_each_cwq_cpu(cpu, wq) {
> - struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
> - struct worker_pool *pool = cwq->pool;
> - struct worker *worker;
> - struct hlist_node *pos;
> - int i;
> -
> - spin_lock_irqsave(&pool->lock, flags);
> - for_each_busy_worker(worker, i, pos, pool) {
> - if (worker->task != current)
> - continue;
> - spin_unlock_irqrestore(&pool->lock, flags);
> - /*
> - * I'm @worker, no locking necessary. See if @work
> - * is headed to the same workqueue.
> - */
> - return worker->current_cwq->wq == wq;
> - }
> - spin_unlock_irqrestore(&pool->lock, flags);
> - }
> - return false;
> + worker = current_wq_worker();
> + /*
> + * Return %true iff I'm a worker execuing a work item on @wq. If
> + * I'm @worker, it's safe to dereference it without locking.
> + */
> + return worker && worker->current_cwq->wq == wq;
> }
>
> static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
> --
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