From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030254AbXDCOVL (ORCPT ); Tue, 3 Apr 2007 10:21:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030274AbXDCOVL (ORCPT ); Tue, 3 Apr 2007 10:21:11 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:54092 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030254AbXDCOVJ (ORCPT ); Tue, 3 Apr 2007 10:21:09 -0400 Date: Tue, 3 Apr 2007 19:31:50 +0530 From: Gautham R Shenoy To: Ingo Molnar Cc: akpm@linux-foundation.org, paulmck@us.ibm.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, vatsa@in.ibm.com, Oleg Nesterov , "Rafael J. Wysocki" , dipankar@in.ibm.com, dino@in.ibm.com, masami.hiramatsu.pt@hitachi.com Subject: Re: [RFC] Cpu-hotplug: Using the Process Freezer (try2) Message-ID: <20070403140150.GA14900@in.ibm.com> Reply-To: ego@in.ibm.com References: <20070402053457.GA9076@in.ibm.com> <20070402061612.GA7072@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070402061612.GA7072@elte.hu> User-Agent: Mutt/1.5.12-2006-07-14 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 02, 2007 at 08:16:12AM +0200, Ingo Molnar wrote: > i'm wondering about how TASK_UNINTERRUPTIBLE tasks are handled by the > freezer: are they assumed frozen immediately, or do we wait until they > notice their PF_FREEZING and go into try_to_freeze()? I'd expect > TASK_UNINTERRUPTIBLE to be the largest source of latency. (and hence be > the primary source for freezing 'failures') Ok, are some luck. I panic()ed on freezer fail and checked the stacktrace of the unfrozen tasks. The stacktrace of each one looks like: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PID: 7697 TASK: cc354a70 CPU: 7 COMMAND: "make" #0 [cc37fe50] schedule at c0431752 #1 [cc37fec4] wait_for_completion at c04318d0 #2 [cc37ff24] do_fork at c01249a6 #3 [cc37ff94] sys_vfork at c0103c1f #4 [cc37ffb4] system_call at c0104d8d ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Rafael had sent out a patch to fix the vfork race, which can be found at http://lkml.org/lkml/2007/3/1/212 However, the following hunk seems to be missing from the latest -mm. @@ -1393,7 +1394,9 @@ long do_fork(unsigned long clone_flags, tracehook_report_clone_complete(clone_flags, nr, p); if (clone_flags & CLONE_VFORK) { + freezer_do_not_count(); wait_for_completion(&vfork); + freezer_count(); tracehook_report_vfork_done(p, nr); } } else { Rafael / Andrew, Any reasons for leaving this hunk out? I reran my tests with this hunk applied, and it work just fine. Even 'make -j' the maximum time taken to hotplug a cpu was 0m2.16s. > > Ingo Thanks and Regards gautham. -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!"