Re: [PATCH] workqueue: don't alloc_percpu for single workqueue

[Eric Dumazet <dada1@cosmosbay.com>]

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;