linux-kernel - Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.

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Message-Id: <20090126133551.fab5e27a.akpm@linux-foundation.org>
Date:	Mon, 26 Jan 2009 13:35:51 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	oleg@...hat.com, a.p.zijlstra@...llo.nl, rusty@...tcorp.com.au,
	travis@....com, mingo@...hat.com, davej@...hat.com,
	cpufreq@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.

On Mon, 26 Jan 2009 22:27:27 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > > So if it's generic it ought to be implemented in a generic way - not a 
> > > "dont use from any codepath that has a lock held that might 
> > > occasionally also be held in a keventd worklet". (which is a totally 
> > > unmaintainable proposition and which would just cause repeat bugs 
> > > again and again.)
> > 
> > That's different.  The core fault here lies in the keventd workqueue 
> > handling code.  If we're flushing work A then we shouldn't go and block 
> > behind unrelated work B.
> 
> the blocking is inherent in the concept of "a queue of worklets handled by 
> a single thread".
> 
> If a worklet is blocked then all other work performed by that thread is 
> blocked as well. So by waiting on a piece of work in the queue, we wait 
> for all prior work queued up there as well.
> 
> The only way to decouple that and to make them independent (and hence 
> independently flushable) is to create more parallel flows of execution: 
> i.e. by creating another thread (another workqueue).
> 

Nope.  As I said, the caller of flush_work() can detach the work item
and run it directly.
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