From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758915AbYEGPB2 (ORCPT ); Wed, 7 May 2008 11:01:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758087AbYEGPBM (ORCPT ); Wed, 7 May 2008 11:01:12 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38078 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757686AbYEGPBJ (ORCPT ); Wed, 7 May 2008 11:01:09 -0400 Date: Wed, 7 May 2008 08:00:04 -0700 (PDT) From: Linus Torvalds To: Alan Cox cc: Andi Kleen , Matthew Wilcox , "Zhang, Yanmin" , Ingo Molnar , LKML , Alexander Viro , Andrew Morton Subject: Re: AIM7 40% regression with 2.6.26-rc1 In-Reply-To: <20080507153538.446693af@core> Message-ID: References: <1210052904.3453.30.camel@ymzhang> <20080506114449.GC32591@elte.hu> <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> <20080507153538.446693af@core> User-Agent: Alpine 1.10 (LFD 962 2008-03-14) 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 On Wed, 7 May 2008, Alan Cox wrote: > > > But my preferred option would indeed be just turning it back into a > > spinlock - and screw latency and BKL preemption - and having the RT people > > who care deeply just work on removing the BKL in the long run. > > It isn't as if the RT build can't use a different lock type to the > default build. Well, considering just *how* bad the new BKL apparently is, I think that's a separate issue. The semaphore implementation is simply not worth it. At a minimum, it should be a mutex. > > Is BKL preemption worth it? Sounds very dubious. Sounds even more dubious > > when we now apparently have even more reason to aim for removing the BKL > > rather than trying to mess around with it. > > We have some horrible long lasting BKL users left unfortunately. Quite frankly, maybe we _need_ to have a bad BKL for those to ever get fixed. As it was, people worked on trying to make the BKL behave better, and it was a failure. Rather than spend the effort on trying to make it work better (at a horrible cost), why not just say "Hell no - if you have issues with it, you need to work with people to get rid of the BKL rather than cluge around it". Linus