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From: David Howells <dhowells@redhat.com>
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Subject: Re: Why Semaphore Hardware-Dependent? 
Date: Tue, 29 Aug 2006 17:25:02 +0100
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Sender: linux-arch-owner@vger.kernel.org
To: Ralf Baechle <ralf@linux-mips.org>
Cc: Christoph Lameter <clameter@sgi.com>, David Howells <dhowells@redhat.com>, Nick Piggin <nickpiggin@yahoo.com.au>, Arjan van de Ven <arjan@infradead.org>, Dong Feng <middle.fengdong@gmail.com>, ak@suse.de, Paul Mackerras <paulus@samba.org>, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
List-ID: <linux-arch.vger.kernel.org>

Ralf Baechle <ralf@linux-mips.org> wrote:

> > Which arches do not support cmpxchg?
> 
> MIPS, Alpha - probably any pure RISC load/store architecture.

Some of these have LL/SC or equivalent instead, but ARM5 and before, FRV, M68K
before 68020 to name but a few.

And anything that implements CMPXCHG with spinlocks is a really bad candidate
for CMPXCHG-based rwsems.

David