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SubjectRe: [PATCH] workqueue: don't alloc_percpu for single workqueue
Lai Jiangshan a écrit :
> allocating memory for every cpu for single workqueue is waste.
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 2f44583..ecd693d 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -99,7 +99,7 @@ static
> struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
> {
> if (unlikely(is_wq_single_threaded(wq)))
> - cpu = singlethread_cpu;
> + return wq->cpu_wq;
> return per_cpu_ptr(wq->cpu_wq, cpu);
> }
>
> @@ -417,7 +417,7 @@ void flush_workqueue(struct workqueue_struct *wq)
> lock_map_acquire(&wq->lockdep_map);
> lock_map_release(&wq->lockdep_map);
> for_each_cpu_mask_nr(cpu, *cpu_map)
> - flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
> + flush_cpu_workqueue(wq_per_cpu(wq, cpu));
> }
> EXPORT_SYMBOL_GPL(flush_workqueue);
>
> @@ -548,7 +548,7 @@ static void wait_on_work(struct work_struct *work)
> cpu_map = wq_cpu_map(wq);
>
> for_each_cpu_mask_nr(cpu, *cpu_map)
> - wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
> + wait_on_cpu_work(wq_per_cpu(wq, cpu), work);
> }
>
> static int __cancel_work_timer(struct work_struct *work,
> @@ -752,17 +752,13 @@ int current_is_keventd(void)
>
> }
>
> -static struct cpu_workqueue_struct *
> -init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
> +static void init_cpu_workqueue(struct workqueue_struct *wq,
> + struct cpu_workqueue_struct *cwq)
> {
> - struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
> -
> cwq->wq = wq;
> spin_lock_init(&cwq->lock);
> INIT_LIST_HEAD(&cwq->worklist);
> init_waitqueue_head(&cwq->more_work);
> -
> - return cwq;
> }
>
> static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
> @@ -816,7 +812,10 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
> if (!wq)
> return NULL;
>
> - wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
> + if (singlethread)
> + wq->cpu_wq = kmalloc(sizeof(*cwq), GFP_KERNEL);

kzalloc() here, since alloc_percpu() does the zeroing for you.

Or else run_depth is not initialized for example.

> + else
> + wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
> if (!wq->cpu_wq) {
> kfree(wq);
> return NULL;


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