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Message-ID: <43A8BA07.4000804@yahoo.com.au>
Date: Wed, 21 Dec 2005 13:12:23 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Nicolas Pitre <nico@cam.org>
CC: Linus Torvalds <torvalds@osdl.org>,
       Russell King <rmk+lkml@arm.linux.org.uk>, Ingo Molnar <mingo@elte.hu>,
       David Woodhouse <dwmw2@infradead.org>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       lkml <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>,
       Arjan van de Ven <arjanv@infradead.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Christoph Hellwig <hch@infradead.org>, Andi Kleen <ak@suse.de>,
       David Howells <dhowells@redhat.com>,
       Alexander Viro <viro@parcelfarce.linux.theplanet.co.uk>,
       Oleg Nesterov <oleg@tv-sign.ru>, Paul Jackson <pj@sgi.com>
Subject: Re: [patch 04/15] Generic Mutex Subsystem, add-atomic-call-func-x86_64.patch
References: <20051219013507.GE27658@elte.hu> <Pine.LNX.4.64.0512190948410.1678@montezuma.fsmlabs.com> <1135025932.4760.1.camel@localhost.localdomain> <20051220043109.GC32039@elte.hu> <Pine.LNX.4.64.0512192358160.26663@localhost.localdomain> <43A7BCE1.7050401@yahoo.com.au> <Pine.LNX.4.64.0512200909180.26663@localhost.localdomain> <43A81132.8040703@yahoo.com.au> <Pine.LNX.4.64.0512200927450.26663@localhost.localdomain> <Pine.LNX.4.64.0512201026230.4827@g5.osdl.org> <20051220193423.GC24199@flint.arm.linux.org.uk> <Pine.LNX.4.64.0512201202200.4827@g5.osdl.org> <Pine.LNX.4.64.0512201533120.26663@localhost.localdomain>
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Nicolas Pitre wrote:
> On Tue, 20 Dec 2005, Linus Torvalds wrote:

>>IOW, why don't you just do
>>
>>	ldr  lr,[%0]
>>	subs lr, lr, %1
>>	str  lr,[%0]
>>	blmi failure
>>
>>as the _base_ timings, since that should be the common case. That's the 
>>drop-dead fastest UP case.
> 
> 
> The above is 5 cycles.  About the same as the preemption-safe swp-based 
> mutex implementation on non-Intel ARM.  It is broken wrt interrupts when 
> the swp is not.

How it is broken WRT interrupts? (sorry, I haven't had it explained to me
in words of two syllables or less)

-- 
SUSE Labs, Novell Inc.

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