Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759962AbZAGRv7 (ORCPT ); Wed, 7 Jan 2009 12:51:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754287AbZAGRvr (ORCPT ); Wed, 7 Jan 2009 12:51:47 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:51324 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751020AbZAGRvq (ORCPT ); Wed, 7 Jan 2009 12:51:46 -0500 Date: Wed, 7 Jan 2009 09:50:57 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Chris Mason cc: Peter Zijlstra , paulmck@linux.vnet.ibm.com, Gregory Haskins , Ingo Molnar , Matthew Wilcox , Andi Kleen , Andrew Morton , Linux Kernel Mailing List , linux-fsdevel , linux-btrfs , Thomas Gleixner , Steven Rostedt , Nick Piggin , Peter Morreale , Sven Dietrich Subject: Re: [PATCH -v4][RFC]: mutex: implement adaptive spinning In-Reply-To: <1231348801.27813.31.camel@think.oraclecorp.com> Message-ID: References: <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> <4963584A.4090805@novell.com> <20090106131643.GA15228@elte.hu> <1231248041.11687.107.camel@twins> <49636799.1010109@novell.com> <20090106214229.GD6741@linux.vnet.ibm.com> <1231278275.11687.111.camel@twins> <1231279660.11687.121.camel@twins> <1231281801.11687.125.camel@twins> <1231283778.11687.136.camel@twins> <1231329783.11687.287.camel@twins> <1231348801.27813.31.camel@think.oraclecorp.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 907 Lines: 24 On Wed, 7 Jan 2009, Chris Mason wrote: > > So far I haven't found any btrfs benchmarks where this is slower than > mutexes without any spinning. But, it isn't quite as fast as the btrfs > spin. Quite frankly, from our history with ext3 and other filesystems, using a mutex in the filesystem is generally the wrong thing to do anyway. Are you sure you can't just use a spinlock, and just release it over IO? The "have to do IO or extend the btree" case is usually pretty damn clear. Because it really sounds like you're lock-limited, and you should just try to clean it up. A pure "just spinlock" in the hotpath is always going to be better. Linus -- 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/