[ltt-dev] [RFC PATCH] Poll : add poll_wait_set_exclusive (fixing thundering herd problem in LTTng)

[KOSAKI Motohiro]

Hi

>  static struct poll_table_entry *poll_get_entry(poll_table *_p)
>  {
>  	struct poll_wqueues *p = container_of(_p, struct poll_wqueues, pt);
> @@ -117,8 +135,10 @@ static struct poll_table_entry *poll_get
>  }
>  
>  /* Add a new entry */
> -static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
> -				poll_table *p)
> +static void __pollwait_common(struct file *filp,
> +			      wait_queue_head_t *wait_address,
> +			      poll_table *p,
> +			      int exclusive)
>  {
>  	struct poll_table_entry *entry = poll_get_entry(p);
>  	if (!entry)
> @@ -127,7 +147,23 @@ static void __pollwait(struct file *filp
>  	entry->filp = filp;
>  	entry->wait_address = wait_address;
>  	init_waitqueue_entry(&entry->wait, current);
> -	add_wait_queue(wait_address, &entry->wait);
> +	if (!exclusive)
> +		add_wait_queue(wait_address, &entry->wait);
> +	else
> +		add_wait_queue_exclusive(wait_address, &entry->wait);
> +}


I fully agreed this feature is needed.
Actually, I've made similar patch at one years ago.

http://marc.info/?l=linux-kernel&m=120257050719087&w=2


but, I have one question.
My version have epoll support, but yours donesn't have.
Is it intensionally?

this is just dumb question, it doesn't mean any objection.