From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <43A21E55.3060907@yahoo.com.au> Date: Fri, 16 Dec 2005 12:54:29 +1100 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation References: <1134560671.2894.30.camel@laptopd505.fenrus.org> <439EDC3D.5040808@nortel.com> <1134479118.11732.14.camel@localhost.localdomain> <3874.1134480759@warthog.cambridge.redhat.com> <15167.1134488373@warthog.cambridge.redhat.com> <1134490205.11732.97.camel@localhost.localdomain> <1134556187.2894.7.camel@laptopd505.fenrus.org> <1134558188.25663.5.camel@localhost.localdomain> <1134558507.2894.22.camel@laptopd505.fenrus.org> <1134559470.25663.22.camel@localhost.localdomain> <20051214033536.05183668.akpm@osdl.org> <15412.1134561432@warthog.cambridge.redhat.com> In-Reply-To: <15412.1134561432@warthog.cambridge.redhat.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit To: David Howells Cc: Arjan van de Ven , Andrew Morton , Alan Cox , cfriesen@nortel.com, torvalds@osdl.org, hch@infradead.org, matthew@wil.cx, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org List-ID: David Howells wrote: > Arjan van de Ven wrote: > > >>> given that >>>mutex_down() is slightly more costly than current down(), and mutex_up() is >>>appreciably more costly than current up()? >> >>that's an implementation flaw in the current implementation that is not >>needed by any means and that Ingo has fixed in his version of this > > > As do I. I wrote it yesterday with Ingo looking over my shoulder, as it were, > but I haven't released it yet. > > What I provided was a base implementation that anything can use provided it > has an atomic op capable of exchanging between two states, and I suspect > everything that can do multiprocessing has - if you can do spinlocks, then you > can do this. I ALSO provided a mechanism by which it could be overridden if > there's something better available on that arch. > > As I see it there are four classes of arch: > > (0) Those that have no atomic ops at all - in which case xchg is trivially > implemented by disabling interrupts, and spinlocks must be null because > they can't be implemented. > > (1) Those that only have a limited exchange functionality. Several archs do > fall into this category: arm, frv, mn10300, 68000, i386. > > (2) Those that have CMPXCHG or equivalent: 68020, i486+, x86_64, ia64, sparc. > > (3) Those that have LL/SC or equivalent: mips (some), alpha, powerpc, arm6. > cmpxchg is basically exactly equivalent to a store-conditional, so 2 and 3 are the same level. I don't know why you don't implement a "good" default implementation with atomic_cmpxchg. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com