linux-kernel - Re: [PATCH UPDATED] workqueue: add documentation

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Message-Id: <20100910104324.6079a0b3.randy.dunlap@oracle.com>
Date:	Fri, 10 Sep 2010 10:43:24 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Florian Mickler <florian@...kler.org>,
	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH UPDATED] workqueue: add documentation

On Fri, 10 Sep 2010 16:55:21 +0200 Tejun Heo wrote:

> +3. The Design

> +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 and more. To

               CPU

> +get a detailed overview refer to the API description of
> +alloc_workqueue() below.

> +4. Application Programming Interface (API)

> +@...gs:
> +
> +  WQ_NON_REENTRANT
> +
> +	By default, a wq guarantees non-reentrance only on the same
> +	CPU.  A work may not be executed concurrently on the same CPU

	        work item

> +	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_CPU_INTENSIVE
> +
> +	Work items of a CPU intensive wq do not contribute to the
> +	concurrency level.  In other words, Runnable CPU intensive

	                                    runnable

> +	work items will not prevent other work items from starting
> +	execution.  This is useful for bound work items which are
> +	expected to hog CPU cycles so that their execution is
> +	regulated by the system scheduler.

---
~Randy
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