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

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Message-Id: <1208196552.4877.30.camel@localhost.localdomain>
Date:	Mon, 14 Apr 2008 11:09:12 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Roland Dreier <rdreier@...co.com>, Ingo Molnar <mingo@...e.hu>,
	Matthew Wilcox <matthew@....cx>,
	Ingo Oeser <ioe-lkml@...eria.de>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [PATCH] Replace completions with semaphores


On Mon, 2008-04-14 at 19:54 +0200, Peter Zijlstra wrote:
> On Mon, 2008-04-14 at 19:46 +0200, Andi Kleen wrote:
> > Peter Zijlstra <peterz@...radead.org> writes:
> > >
> > > Yeah, I would open code it.  But this is indeed a sane usage of the
> > > counting semaphore because there is no priority inversion.
> > 
> > But when you open code that, how is it different from just having
> > semaphores? 
> 
> Because we can then eventually get rid of semaphores, so those people
> cannot mistakenly use them. Its just too easy to create prio inversion
> with them around.

I'm not for open coding anything .. This "writes in flight" type code
happens often enough we should have something that covers it..
completions come fairly close (since they're just like locked
semaphores) only it's not easy to initialize them to allow multiple
completes before the waiting starts..

Daniel

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