From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Thu, 17 Oct 2002 16:13:24 +0200 (CEST) Received: from buserror-extern.convergence.de ([212.84.236.66]:21508 "EHLO hell") by linux-mips.org with ESMTP id ; Thu, 17 Oct 2002 16:13:24 +0200 Received: from js by hell with local (Exim 3.35 #1 (Debian)) id 182BOY-0000Xj-00; Thu, 17 Oct 2002 16:13:02 +0200 Date: Thu, 17 Oct 2002 16:13:02 +0200 From: Johannes Stezenbach To: "Gleb O. Raiko" Cc: "Maciej W. Rozycki" , "Kevin D. Kissell" , linux-mips@linux-mips.org Subject: Re: Once again: test_and_set for CPUs w/o LL/SC Message-ID: <20021017141302.GA2039@convergence.de> Mail-Followup-To: Johannes Stezenbach , "Gleb O. Raiko" , "Maciej W. Rozycki" , "Kevin D. Kissell" , linux-mips@linux-mips.org References: <3DAE872E.D5EF0E4D@niisi.msk.ru> <20021017131115.GA1689@convergence.de> <3DAEBBD3.333275FC@niisi.msk.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3DAEBBD3.333275FC@niisi.msk.ru> User-Agent: Mutt/1.4i Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 474 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: js@convergence.de Precedence: bulk X-list: linux-mips On Thu, Oct 17, 2002 at 05:32:03PM +0400, Gleb O. Raiko wrote: > Johannes Stezenbach wrote: > > > > On Thu, Oct 17, 2002 at 02:02:35PM +0200, Maciej W. Rozycki wrote: > > > On Thu, 17 Oct 2002, Gleb O. Raiko wrote: > > > > > > > Implement new sysmips then. > > > > > > I'm not sure if that's a good idea. Glibc alone uses test_and_set(), > > > exchange_and_add(), atomic_add() and compare_and_swap(). Do you want a > > > separate syscall for each of these functions? I think the ll/sc emulation > > > may be the best solution after all. At least it's most flexible and not > > > much slower if at all. > > > > Depends on your usage pattern. E.g. we don't run software that uses > > atomicity.h (i.e. no C++ code), but heavily use pthread_mutex_lock() etc. > > The few uses of atomicity.h internal to glibc don't warrant > > any optimizations. So, if the beql-Method would not exist, I would > > consider implementing a new sysmips for compare_and_swap(). > > I didn't look at newer glibc sources (read: greater than 2.0.6), so the > question. Why is the difference between compare_and_swap and > test_and_set so huge that it eats an exception penalty? ;-) It is not. I wrote: ... But with LL/SC glibc can use compare-and-swap which enables a more efficient linux-threads mutex implementation. This is what makes the difference, at least for glibc-2.2.5. Just grep for HAS_COMPARE_AND_SWAP in your linuxthreads sources. Current glibc from CVS (both HEAD an 2.2 branch) doesn't use sysmips anymore, they rely on LL/SC (emulated or not). Regards, Johannes