linux-kernel - Re: [PATCH 1/9] workqueue: mark WQ_NON

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Date:	Wed, 31 Jul 2013 14:12:29 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org, shli@...nel.org
Subject: Re: [PATCH 1/9] workqueue: mark WQ_NON_REENTRANT deprecated

On 07/30/2013 08:40 PM, Tejun Heo wrote:
> dbf2576e37 ("workqueue: make all workqueues non-reentrant") made
> WQ_NON_REENTRANT no-op but the following patches didn't remove the
> flag or update the documentation.  Let's mark the flag deprecated and
> update the documentation accordingly.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>

Acked-by: Lai Jiangshan <laijs@...fujitsu.com>

> ---
>  Documentation/workqueue.txt | 18 ++++++------------
>  include/linux/workqueue.h   |  7 ++++++-
>  2 files changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/workqueue.txt b/Documentation/workqueue.txt
> index a6ab4b6..67113f6 100644
> --- a/Documentation/workqueue.txt
> +++ b/Documentation/workqueue.txt
> @@ -100,8 +100,8 @@ Subsystems and drivers can create and queue work items through special
>  workqueue API functions as they see fit. They can influence some
>  aspects of the way the work items are executed by setting flags on the
>  workqueue they are putting the work item on. These flags include
> -things like CPU locality, reentrancy, concurrency limits, priority and
> -more.  To get a detailed overview refer to the API description of
> +things like CPU locality, concurrency limits, priority and more.  To
> +get a detailed overview refer to the API description of
>  alloc_workqueue() below.
>  
>  When a work item is queued to a workqueue, the target gcwq and
> @@ -166,16 +166,6 @@ resources, scheduled and executed.
>  
>  @flags:
>  
> -  WQ_NON_REENTRANT
> -
> -	By default, a wq guarantees non-reentrance only on the same
> -	CPU.  A work item may not be executed concurrently on the same
> -	CPU by multiple workers but is allowed to be executed
> -	concurrently on multiple CPUs.  This flag makes sure
> -	non-reentrance is enforced across all CPUs.  Work items queued
> -	to a non-reentrant wq are guaranteed to be executed by at most
> -	one worker system-wide at any given time.
> -
>    WQ_UNBOUND
>  
>  	Work items queued to an unbound wq are served by a special
> @@ -233,6 +223,10 @@ resources, scheduled and executed.
>  
>  	This flag is meaningless for unbound wq.
>  
> +Note that the flag WQ_NON_REENTRANT no longer exists as all workqueues
> +are now non-reentrant - any work item is guaranteed to be executed by
> +at most one worker system-wide at any given time.
> +
>  @max_active:
>  
>  @max_active determines the maximum number of execution contexts per
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index a0ed78a..594521b 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -295,7 +295,12 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
>   * Documentation/workqueue.txt.
>   */
>  enum {
> -	WQ_NON_REENTRANT	= 1 << 0, /* guarantee non-reentrance */
> +	/*
> +	 * All wqs are now non-reentrant making the following flag
> +	 * meaningless.  Will be removed.
> +	 */
> +	WQ_NON_REENTRANT	= 1 << 0, /* DEPRECATED */
> +
>  	WQ_UNBOUND		= 1 << 1, /* not bound to any cpu */
>  	WQ_FREEZABLE		= 1 << 2, /* freeze during suspend */
>  	WQ_MEM_RECLAIM		= 1 << 3, /* may be used for memory reclaim */

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