From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765043AbYEGRgn (ORCPT ); Wed, 7 May 2008 13:36:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755001AbYEGRga (ORCPT ); Wed, 7 May 2008 13:36:30 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:49958 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754982AbYEGRg2 (ORCPT ); Wed, 7 May 2008 13:36:28 -0400 Date: Wed, 7 May 2008 19:36:12 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Andi Kleen , Matthew Wilcox , "Zhang, Yanmin" , LKML , Alexander Viro , Andrew Morton Subject: Re: AIM7 40% regression with 2.6.26-rc1 Message-ID: <20080507173612.GA13591@elte.hu> References: <1210126286.3453.37.camel@ymzhang> <1210131712.3453.43.camel@ymzhang> <87lk2mbcqp.fsf@basil.nowhere.org> <20080507114643.GR19219@parisc-linux.org> <87hcdab8zp.fsf@basil.nowhere.org> <20080507162012.GA10096@elte.hu> <20080507170528.GA11511@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Linus Torvalds wrote: > > > On Wed, 7 May 2008, Ingo Molnar wrote: > > > > it was removed by me in the course of this discussion: > > > > http://lkml.org/lkml/2008/1/2/58 > > > > the whole discussion started IIRC because !CONFIG_PREEMPT_BKL [the > > spinlock version] was broken for a longer period of time (it crashed > > trivially), because nobody apparently used it. > > Hmm. I've generally used PREEMPT_NONE, and always thought PREEMPT_BKL > was the known-flaky one. > > The thread you point to also says that it's PREEMPT_BKL=y that was the > problem (ie "I've seen 1s+ desktop latencies due to PREEMPT_BKL when I > was still using reiserfs."), not the plain spinlock approach. no, there was another problem (which i couldnt immediately find because lkml.org only indexes part of the threads, i'll research it some more), which was some cond_resched() thing in the !PREEMPT_BKL case. > But it would definitely be interesting to see the crash reports. And > the help message always said "Say N if you are unsure." even if it > ended up being marked 'y' by default at some point (and then in > January was made first unconditional, and then removed entirely) > > Because in many ways, the non-preempt BKL is the *much* simpler case. > I don't see why it would crash - it just turns the BKL into a trivial > counting spinlock that can sleep. yeah. The latencies are a different problem, and indeed were reported against PREEMPT_BKL, and believed to be due to reiser3 and the tty code. (reiser3 runs almost all of its code under the BKL) The !PREEMPT_BKL crash was some simple screwup on my part of getting atomicity checks wrong in cond_resched() - and it went unnoticed for a long time - or something like that. I'll try to find that discussion. Ingo