linux-kernel - Re: [PATCH 2/3] wait: Return number of exclusive waiters awaken

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Date:   Wed, 16 Nov 2022 12:06:03 +0100
From:   Jan Kara <jack@...e.cz>
To:     Gabriel Krisman Bertazi <krisman@...e.de>
Cc:     axboe@...nel.dk, mingo@...hat.com, peterz@...radead.org,
        jack@...e.cz, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, liusong@...ux.alibaba.com,
        chaitanyak@...dia.com
Subject: Re: [PATCH 2/3] wait: Return number of exclusive waiters awaken

On Tue 15-11-22 17:45:52, Gabriel Krisman Bertazi wrote:
> Sbitmap code will need to know how many waiters were actually woken for
> its batched wakeups implementation.  Return the number of woken
> exclusive waiters from __wake_up() to facilitate that.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...e.de>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  include/linux/wait.h |  2 +-
>  kernel/sched/wait.c  | 18 +++++++++++-------
>  2 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/wait.h b/include/linux/wait.h
> index 7f5a51aae0a7..a0307b516b09 100644
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -209,7 +209,7 @@ __remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq
>  	list_del(&wq_entry->entry);
>  }
>  
> -void __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
> +int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
>  void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key);
>  void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
>  		unsigned int mode, void *key, wait_queue_entry_t *bookmark);
> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
> index 9860bb9a847c..133b74730738 100644
> --- a/kernel/sched/wait.c
> +++ b/kernel/sched/wait.c
> @@ -121,11 +121,12 @@ static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
>  	return nr_exclusive;
>  }
>  
> -static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
> +static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
>  			int nr_exclusive, int wake_flags, void *key)
>  {
>  	unsigned long flags;
>  	wait_queue_entry_t bookmark;
> +	int remaining = nr_exclusive;
>  
>  	bookmark.flags = 0;
>  	bookmark.private = NULL;
> @@ -134,10 +135,12 @@ static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int
>  
>  	do {
>  		spin_lock_irqsave(&wq_head->lock, flags);
> -		nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
> +		remaining = __wake_up_common(wq_head, mode, remaining,
>  						wake_flags, key, &bookmark);
>  		spin_unlock_irqrestore(&wq_head->lock, flags);
>  	} while (bookmark.flags & WQ_FLAG_BOOKMARK);
> +
> +	return nr_exclusive - remaining;
>  }
>  
>  /**
> @@ -147,13 +150,14 @@ static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int
>   * @nr_exclusive: how many wake-one or wake-many threads to wake up
>   * @key: is directly passed to the wakeup function
>   *
> - * If this function wakes up a task, it executes a full memory barrier before
> - * accessing the task state.
> + * If this function wakes up a task, it executes a full memory barrier
> + * before accessing the task state.  Returns the number of exclusive
> + * tasks that were awaken.
>   */
> -void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
> -			int nr_exclusive, void *key)
> +int __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
> +	      int nr_exclusive, void *key)
>  {
> -	__wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
> +	return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
>  }
>  EXPORT_SYMBOL(__wake_up);
>  
> -- 
> 2.35.3
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR