Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751370AbWKBSrD (ORCPT ); Thu, 2 Nov 2006 13:47:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752033AbWKBSrD (ORCPT ); Thu, 2 Nov 2006 13:47:03 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:32394 "EHLO e34.co.us.ibm.com") by vger.kernel.org with ESMTP id S1751370AbWKBSrB (ORCPT ); Thu, 2 Nov 2006 13:47:01 -0500 Date: Fri, 3 Nov 2006 00:16:37 +0530 From: Dipankar Sarma To: Dave Jones , Linus Torvalds , Linux Kernel , Andrew Morton , Gautham Shenoy Subject: Re: Remove hotplug cpu crap from cpufreq. Message-ID: <20061102184637.GA23489@in.ibm.com> Reply-To: dipankar@in.ibm.com References: <20061101225925.GA17363@redhat.com> <20061101233250.GA17706@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061101233250.GA17706@redhat.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2090 Lines: 51 Dave, On Wed, Nov 01, 2006 at 06:32:50PM -0500, Dave Jones wrote: > On Wed, Nov 01, 2006 at 03:09:52PM -0800, Linus Torvalds wrote: > > > Hmm. People _have_ given a damn, and I think you were even cc'd. > > You're right. In my defense, that stuff arrived the day I went > on vacation for two weeks, and I subsequently forgot all about it. > Looking back over that thread though, a few people seemed to pick a > number of holes in the patches, and there are some real gems in that > thread like. Have you looked at this patchset - http://lkml.org/lkml/2006/10/26/65 ? This is the latest patchset posted last week and I haven't seen any comments on it. > > Really, the hotplug locking rules are fairly simple- > > > > 1. If you are in cpu hotplug callback path, don't take any lock. > > Which is just great, as afair, the cpufreq locks were there _before_ > someone liberally sprinkled lock_cpu_hotplug() everywhere. This one has a major *cleanup* of cpufreq code including removel of unncessary lock_cpu_hotplug() from cpufreq. > > From what I can tell from looking at that thread back in August, > it went on for a while with a number of people picking holes in the > proposed patches, but there wasn't any reposted after that, and > certainly nothing that ended up in -mm. > > _something_ needs to be done. If someone wants to fix it, great, but > until we see something mergable, we're left in this half-assed state > which is freaking people out. There are two approaches - Implicit hotplug callback order-based locking as Andrew has done or keep the current cpu hotplug "lock" semantics and just use a better lock (RCU-based) with cpu-local access in the fast path. Gautham's patchset does the latter. lock_cpu_hotplug() is a misnomer, we should probably use get_cpu_hotplug() and put_cpu_hotplug() there. Thanks Dipankar - 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/