Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261913AbVASVtN (ORCPT ); Wed, 19 Jan 2005 16:49:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261921AbVASVry (ORCPT ); Wed, 19 Jan 2005 16:47:54 -0500 Received: from ozlabs.org ([203.10.76.45]:26337 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S261913AbVASVn3 (ORCPT ); Wed, 19 Jan 2005 16:43:29 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <16878.54402.344079.528038@cargo.ozlabs.ibm.com> Date: Thu, 20 Jan 2005 08:43:30 +1100 From: Paul Mackerras To: Ingo Molnar Cc: Peter Chubb , Tony Luck , Darren Williams , Andrew Morton , Chris Wedgwood , torvalds@osdl.org, benh@kernel.crashing.org, linux-kernel@vger.kernel.org, Ia64 Linux , Christoph Hellwig Subject: Re: Horrible regression with -CURRENT from "Don't busy-lock-loop in preemptable spinlocks" patch In-Reply-To: <20050119092013.GA2045@elte.hu> References: <20050117055044.GA3514@taniwha.stupidest.org> <20050116230922.7274f9a2.akpm@osdl.org> <20050117143301.GA10341@elte.hu> <20050118014752.GA14709@cse.unsw.EDU.AU> <16877.42598.336096.561224@wombat.chubb.wattle.id.au> <20050119080403.GB29037@elte.hu> <16878.9678.73202.771962@wombat.chubb.wattle.id.au> <20050119092013.GA2045@elte.hu> X-Mailer: VM 7.19 under Emacs 21.3.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1357 Lines: 36 Ingo Molnar writes: > * Peter Chubb wrote: > > > >> Here's a patch that adds the missing read_is_locked() and > > >> write_is_locked() macros for IA64. When combined with Ingo's > > >> patch, I can boot an SMP kernel with CONFIG_PREEMPT on. > > >> > > >> However, I feel these macros are misnamed: read_is_locked() returns > > >> true if the lock is held for writing; write_is_locked() returns > > >> true if the lock is held for reading or writing. > > > > Ingo> well, 'read_is_locked()' means: "will a read_lock() succeed" > > > > Fail, surely? > > yeah ... and with that i proved beyond doubt that the naming is indeed > unintuitive :-) Yes. Intuitively read_is_locked() is true when someone has done a read_lock and write_is_locked() is true when someone has done a write lock. I suggest read_poll(), write_poll(), spin_poll(), which are like {read,write,spin}_trylock but don't do the atomic op to get the lock, that is, they don't change the lock value but return true if the trylock would succeed, assuming no other cpu takes the lock in the meantime. Regards, Paul. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/