linux-kernel - Re: [PATCH] Replace completions with semaphores

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Message-Id: <200804161842.52739.oliver@neukum.org>
Date:	Wed, 16 Apr 2008 18:42:50 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Ingo Oeser <ioe-lkml@...eria.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Bart Van Assche <bart.vanassche@...il.com>,
	Roland Dreier <rdreier@...co.com>, Ingo Molnar <mingo@...e.hu>,
	Daniel Walker <dwalker@...sta.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Replace completions with semaphores

Am Mittwoch, 16. April 2008 18:34:14 schrieb Matthew Wilcox:
> On Wed, Apr 16, 2008 at 06:31:08PM +0200, Oliver Neukum wrote:
> > Am Mittwoch, 16. April 2008 18:16:52 schrieb Matthew Wilcox:
> > > The basic idea is that you get back a cookie from the kcounter_claim()
> > > which you have to hand to the kcounter_release() function so it
> > > knows which one you released. ?It's similar to mutex debugging except
> > 
> > So in addition to the kcounter we need to save a token in a data structure?
> > In fact, there must be a data structure that can house that token. So you
> > can no longer live with a pointer just to a device descriptor, but every
> > individual use of a resource must have an associated data structure?
> 
> That's right.  Do you have an example where this would be inconvenient?
> I couldn't find one.  For example, with USB, you could place one in the
> struct urb.

That's a data structure we really want to shrink. And furthermore, the needs
of the use cases should shape the locking primitives, not the reverse.

	Regards
		Oliver
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