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

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Message-ID: <alpine.LFD.1.00.0804150952300.2879@woody.linux-foundation.org>
Date:	Tue, 15 Apr 2008 09:57:07 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Bart Van Assche <bart.vanassche@...il.com>,
	Roland Dreier <rdreier@...co.com>, Ingo Molnar <mingo@...e.hu>,
	Matthew Wilcox <matthew@....cx>,
	Ingo Oeser <ioe-lkml@...eria.de>,
	Daniel Walker <dwalker@...sta.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Replace completions with semaphores

On Tue, 15 Apr 2008, Andi Kleen wrote:
> 
> >  - probably add support for completions to do counting
> 
> But that's just a semaphore, isn't it?

Exactly. But the point here is:

 - nobody should use semaphores anyway (use mutexes)
 - making *more* code use semaphores is wrong
 - completions have a different _mental_ model

IOW, this is not about implementation issues. It's about how you think 
about the operations.

We should _not_ implement completions as semaphores, simply because we 
want to get *rid* of semaphores some day. 

So rather than this long and involved patch series that first makes 
semaphores generic, and then makes them be used as completions, I'd much 
rather just skip this whole pointless exercise entirely. 

Why have "generic semaphores" at all, if we want to get rid of them? 

		Linus
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