Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752255AbWKBTFP (ORCPT ); Thu, 2 Nov 2006 14:05:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752258AbWKBTFO (ORCPT ); Thu, 2 Nov 2006 14:05:14 -0500 Received: from e2.ny.us.ibm.com ([32.97.182.142]:10163 "EHLO e2.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1752256AbWKBTFN (ORCPT ); Thu, 2 Nov 2006 14:05:13 -0500 Date: Fri, 3 Nov 2006 00:34:50 +0530 From: Dipankar Sarma To: Andrew Morton Cc: Linus Torvalds , Dave Jones , Linux Kernel , Gautham Shenoy Subject: Re: Remove hotplug cpu crap from cpufreq. Message-ID: <20061102190450.GB23489@in.ibm.com> Reply-To: dipankar@in.ibm.com References: <20061101225925.GA17363@redhat.com> <20061101161723.f132d208.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061101161723.f132d208.akpm@osdl.org> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1473 Lines: 36 Andrew, On Wed, Nov 01, 2006 at 04:17:23PM -0800, Andrew Morton wrote: > On Wed, 1 Nov 2006 15:09:52 -0800 (PST) > Linus Torvalds wrote: > > Gautham's work is "add lots of complex machinery so cpufreq's existing crap > works as it was supposed to". We end up with complex machinery as well as > crappy cpufreq. > > The alternative is to rip all that stuff out of cpufreq and then go back > and reimplement cpufreq cpu-hotplug safety from scratch. No matter what we do with cpufreq, cpufreq needs to protect itself against the cpu going away. I am not too confident about the long term viability of the implicit callback order-based locking. Sooner or later, someone will add another complex per-cpu subsystem with calls to another per-cpu subsystem and will violate locking order between the two subsystems. IMO, the right thing to do would be to convert lock_cpu_hotplug() to a get_cpu_hotplug()/put_cpu_hotplug() type semantics and use a more scalable implementation underneath (as opposed to a global semaphore/mutex). We have had some discussion on taking a look at the overall design of the cpufreq and its cpu drivers themselves, but we need solve this issue in the short term. 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/