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

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Date:	Mon, 26 Jan 2009 22:45:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
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.


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> 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.

that would change the concept of execution but indeed it would be 
interesting to try. It's outside the scope of late -rcs i guess, but 
worthwile nevertheless.

	Ingo
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