From: David Miller <davem@davemloft.net>
To: sparclinux@vger.kernel.org
Subject: Re: [RFT] [SPARC] Emulate cmpxchg like parisc
Date: Mon, 28 May 2007 03:16:45 +0000 [thread overview]
Message-ID: <20070527.201645.63127984.davem@davemloft.net> (raw)
In-Reply-To: <20070525201143.GB14171@fattire.cabal.ca>
From: Kyle McMartin <kyle@parisc-linux.org>
Date: Sun, 27 May 2007 23:11:14 -0400
> Yeah, David Howells wanted to use cmpxchg in his work struct patch, but
> had to not because not everyone implements it.
>
> >From what I can tell, very few arches actually have CAS, and others
> emulate it with LL/SC type implementations.
That's fine, as a LL/SC implementation of cmpxchg() is fully
atomic and would work in concert with a userspace cmpxchg()
implemented with LL/SC.
It's the platforms that lack CAS _and_ some kind of LL/SC
which are problematic.
Sparc32 SMP cpus (sparcv8 sun4m and later) have a 'swap' instruction
but that does not have an inifinite consensus number like CAS and
LL/SC, so it can't be used to implement cmpxchg() (and also the
non-SMP sparc32 chips lack the instruction).
next prev parent reply other threads:[~2007-05-28 3:16 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-25 20:11 [RFT] [SPARC] Emulate cmpxchg like parisc Kyle McMartin
2007-05-26 0:24 ` Martin Habets
2007-05-26 5:00 ` David Miller
2007-05-26 5:14 ` Tom "spot" Callaway
2007-05-26 14:45 ` Kyle McMartin
2007-05-26 19:39 ` Martin Habets
2007-05-26 20:32 ` Dave Airlie
2007-05-26 22:46 ` David Miller
2007-05-26 22:59 ` David Miller
2007-05-26 23:00 ` David Miller
2007-05-26 23:41 ` Kyle McMartin
2007-05-27 0:04 ` David Miller
2007-05-28 0:07 ` Martin Habets
2007-05-28 2:49 ` David Miller
2007-05-28 3:11 ` Kyle McMartin
2007-05-28 3:16 ` David Miller [this message]
2007-05-28 23:37 ` Martin Habets
2007-05-29 8:12 ` David Miller
2007-05-29 13:18 ` Kyle McMartin
2007-05-29 20:30 ` Martin Habets
2007-05-29 20:59 ` David Miller
2007-05-29 21:08 ` Kyle McMartin
2007-05-30 19:38 ` Martin Habets
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