From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965007AbVLQXRy (ORCPT ); Sat, 17 Dec 2005 18:17:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965003AbVLQXRy (ORCPT ); Sat, 17 Dec 2005 18:17:54 -0500 Received: from dsl027-180-168.sfo1.dsl.speakeasy.net ([216.27.180.168]:33976 "EHLO sunset.davemloft.net") by vger.kernel.org with ESMTP id S965002AbVLQXRx (ORCPT ); Sat, 17 Dec 2005 18:17:53 -0500 Date: Sat, 17 Dec 2005 15:05:35 -0800 (PST) Message-Id: <20051217.150535.122244453.davem@davemloft.net> To: rth@twiddle.net Cc: torvalds@osdl.org, dhowells@redhat.com, nickpiggin@yahoo.com.au, arjan@infradead.org, akpm@osdl.org, alan@lxorguk.ukuu.org.uk, cfriesen@nortel.com, hch@infradead.org, matthew@wil.cx, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation From: "David S. Miller" In-Reply-To: <20051217223824.GA16736@twiddle.net> References: <20051216.145306.132052494.davem@davemloft.net> <20051217223824.GA16736@twiddle.net> X-Mailer: Mew version 4.2.53 on Emacs 21.4 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Richard Henderson Date: Sat, 17 Dec 2005 14:38:24 -0800 > You might consider just beginning your loops like > > mov zero, old > cas [mem], zero, old > > to do the initial read, since old will now contain the > contents of the memory, and we havn't changed the memory. CAS is 32 cycles minimum on sparc64 even on a cache hit, so I think the prefetch+load will be faster :-) But it deserves checking out, that's for sure. Either way, that is a clever use of CAS :)