Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753850AbZAJRxL (ORCPT ); Sat, 10 Jan 2009 12:53:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752140AbZAJRwz (ORCPT ); Sat, 10 Jan 2009 12:52:55 -0500 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:38925 "EHLO gprs189-60.eurotel.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751540AbZAJRwy (ORCPT ); Sat, 10 Jan 2009 12:52:54 -0500 Date: Sat, 10 Jan 2009 18:52:41 +0100 From: Pavel Machek To: Ingo Molnar Cc: Peter Zijlstra , Matthew Wilcox , Andi Kleen , Chris Mason , Andrew Morton , linux-kernel@vger.kernel.org, linux-fsdevel , linux-btrfs , Thomas Gleixner , Steven Rostedt , Gregory Haskins , Nick Piggin , Linus Torvalds Subject: Re: [PATCH][RFC]: mutex: adaptive spin Message-ID: <20090110175240.GA1436@ucw.cz> References: <1230722935.4680.5.camel@think.oraclecorp.com> <20081231104533.abfb1cf9.akpm@linux-foundation.org> <1230765549.7538.8.camel@think.oraclecorp.com> <87r63ljzox.fsf@basil.nowhere.org> <20090103191706.GA2002@parisc-linux.org> <1231093310.27690.5.camel@twins> <20090104184103.GE2002@parisc-linux.org> <1231242031.11687.97.camel@twins> <20090106121052.GA27232@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090106121052.GA27232@elte.hu> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1118 Lines: 25 > Linus, what do you think about this particular approach of spin-mutexes? > It's not the typical spin-mutex i think. > > The thing i like most about Peter's patch (compared to most other adaptive > spinning approaches i've seen, which all sucked as they included various > ugly heuristics complicating the whole thing) is that it solves the "how > long should we spin" question elegantly: we spin until the owner runs on a > CPU. Well; if there's a timeout, that's obviously safe. But this has no timeout, and Linus wants to play games with accessing 'does owner run on cpu?' lockless. Now, can it mistakenly spin when the owner is scheduled away? That would deadlock, and without locking, I'm not sure if we prevent that.... -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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/