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Home » Mailing list archives » linux-kernel » 2008 » April » 13

Re: [PATCH] Replace completions with semaphores

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From: Ingo Molnar <mingo@...>
To: Peter Zijlstra <peterz@...>
Cc: Matthew Wilcox <matthew@...>, <linux-kernel@...>, Linus Torvalds <torvalds@...>
Subject: Re: [PATCH] Replace completions with semaphores
Date: Sunday, April 13, 2008 - 3:05 am

* Peter Zijlstra <peterz@infradead.org> wrote:


exactly. I first misread the subject line because i parsed it as 
"replace semaphores with completions" and i thought "cool", then did i 
realize that the patch does it the other way around. Converting 
completions to semaphores just makes no sense.

Besides all your arguments later in this thread about how problematic 
locking primitives semaphores are because they are so vague (which are 
all correct), there's also another aspect: completions are faster a bit 
in theory, because they know that they will schedule most of the time - 
while semaphores assume that they will _not_ schedule. (And that's 
exactly because the intent of the developer when using a completion is 
crystal clear.)

	Ingo
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Messages in current thread:
[PATCH] Replace completions with semaphores, Matthew Wilcox, (Fri Apr 11, 5:00 pm)
Re: [PATCH] Replace completions with semaphores, Peter Zijlstra, (Sat Apr 12, 8:24 am)
Re: [PATCH] Replace completions with semaphores, Ingo Molnar, (Sun Apr 13, 3:05 am)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Sun Apr 13, 8:52 am)
Re: [PATCH] Replace completions with semaphores, Jens Axboe, (Mon Apr 14, 12:54 pm)
Re: [PATCH] Replace completions with semaphores, Ingo Molnar, (Mon Apr 14, 11:41 am)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Mon Apr 14, 1:46 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Sat Apr 12, 1:26 pm)
Re: [PATCH] Replace completions with semaphores, Roland Dreier, (Sat Apr 12, 3:53 pm)
Re: [PATCH] Replace completions with semaphores, Bart Van Assche, (Sun Apr 13, 9:55 am)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Sun Apr 13, 10:22 am)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Sat Apr 12, 4:47 pm)
Re: [PATCH] Replace completions with semaphores, Ingo Molnar, (Sun Apr 13, 3:08 am)
Re: [PATCH] Replace completions with semaphores, Bart Van Assche, (Sun Apr 13, 10:55 am)
Re: API documentation (was [PATCH] Replace completions with ..., Jonathan Corbet, (Mon Apr 14, 1:12 pm)
Re: API documentation (was [PATCH] Replace completions with ..., Peter Zijlstra, (Mon Apr 14, 1:33 pm)
Re: API documentation (was [PATCH] Replace completions with ..., Bart Van Assche, (Mon Apr 14, 2:38 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Sun Apr 13, 8:57 am)
Re: [PATCH] Replace completions with semaphores, Ingo Molnar, (Mon Apr 14, 11:39 am)
Re: [PATCH] Replace completions with semaphores, Roland Dreier, (Mon Apr 14, 11:58 am)
Re: [PATCH] Replace completions with semaphores, Peter Zijlstra, (Mon Apr 14, 12:32 pm)
Re: [PATCH] Replace completions with semaphores, Andi Kleen, (Mon Apr 14, 1:46 pm)
Re: [PATCH] Replace completions with semaphores, Peter Zijlstra, (Mon Apr 14, 1:54 pm)
Re: [PATCH] Replace completions with semaphores, Alan Cox, (Mon Apr 14, 3:16 pm)
Re: [PATCH] Replace completions with semaphores, Andi Kleen, (Mon Apr 14, 3:16 pm)
Re: [PATCH] Replace completions with semaphores, Bart Van Assche, (Tue Apr 15, 2:18 am)
Re: [PATCH] Replace completions with semaphores, Peter Zijlstra, (Tue Apr 15, 2:46 am)
Re: [PATCH] Replace completions with semaphores, Bart Van Assche, (Tue Apr 15, 3:17 am)
Re: [PATCH] Replace completions with semaphores, Peter Zijlstra, (Tue Apr 15, 4:44 am)
Re: [PATCH] Replace completions with semaphores, Linus Torvalds, (Tue Apr 15, 12:09 pm)
Re: [PATCH] Replace completions with semaphores, Andi Kleen, (Tue Apr 15, 12:27 pm)
Re: [PATCH] Replace completions with semaphores, Linus Torvalds, (Tue Apr 15, 12:57 pm)
Re: [PATCH] Replace completions with semaphores, Andi Kleen, (Tue Apr 15, 1:15 pm)
Re: [PATCH] Replace completions with semaphores, Linus Torvalds, (Tue Apr 15, 1:26 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Tue Apr 15, 1:41 pm)
Re: [PATCH] Replace completions with semaphores, Linus Torvalds, (Tue Apr 15, 2:14 pm)
Re: [PATCH] Replace completions with semaphores, Ingo Oeser, (Wed Apr 16, 12:07 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Wed Apr 16, 12:16 pm)
Re: [PATCH] Replace completions with semaphores, Oliver Neukum, (Wed Apr 16, 12:31 pm)
Re: [PATCH] Replace completions with semaphores, Arjan van de Ven, (Wed Apr 16, 12:50 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Wed Apr 16, 12:58 pm)
Re: [PATCH] Replace completions with semaphores, Arjan van de Ven, (Wed Apr 16, 1:08 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Wed Apr 16, 2:10 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Wed Apr 16, 1:12 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Wed Apr 16, 12:34 pm)
Re: [PATCH] Replace completions with semaphores, Oliver Neukum, (Wed Apr 16, 12:42 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Wed Apr 16, 12:44 pm)
Re: [PATCH] Replace completions with semaphores, Roland Dreier, (Wed Apr 16, 12:47 pm)
Re: [PATCH] Replace completions with semaphores, Ingo Molnar, (Tue Apr 15, 1:05 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Tue Apr 15, 2:50 pm)
Re: [PATCH] Replace completions with semaphores, Ingo Molnar, (Wed Apr 16, 8:37 am)
Re: [PATCH] Replace completions with semaphores, Andi Kleen, (Wed Apr 16, 8:50 am)
Killable stat/readdir, Matthew Wilcox, (Wed Apr 16, 8:59 am)
Re: [PATCH] Replace completions with semaphores, Bart Van Assche, (Tue Apr 15, 9:15 am)
Re: [PATCH] Replace completions with semaphores, Daniel Walker, (Mon Apr 14, 2:09 pm)
Re: [PATCH] Replace completions with semaphores, Arjan van de Ven, (Mon Apr 14, 12:56 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Mon Apr 14, 1:50 pm)
Re: [PATCH] Replace completions with semaphores, Peter Zijlstra, (Sat Apr 12, 2:05 pm)
Re: [PATCH] Replace completions with semaphores, Matthew Wilcox, (Sat Apr 12, 3:04 pm)
Re: [PATCH] Replace completions with semaphores, Peter Zijlstra, (Sat Apr 12, 3:16 pm)
Re: [PATCH] Replace completions with semaphores, Daniel Walker, (Sat Apr 12, 2:01 pm)
Re: [PATCH] Replace completions with semaphores, Daniel Walker, (Sat Apr 12, 2:43 am)
Re: [PATCH] Replace completions with semaphores, Ingo Oeser, (Sat Apr 12, 6:31 am)

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