From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755282AbYDEVER (ORCPT ); Sat, 5 Apr 2008 17:04:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753932AbYDEVED (ORCPT ); Sat, 5 Apr 2008 17:04:03 -0400 Received: from mtaout03-winn.ispmail.ntl.com ([81.103.221.49]:9279 "EHLO mtaout03-winn.ispmail.ntl.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753674AbYDEVEB convert rfc822-to-8bit (ORCPT ); Sat, 5 Apr 2008 17:04:01 -0400 Date: Sat, 5 Apr 2008 22:03:47 +0100 From: Ken Moffat To: Srivatsa Vaddagiri Cc: Ingo Molnar , "Rafael J. Wysocki" , lkml , a.p.zijlstra@chello.nl, aneesh.kumar@linux.vnet.ibm.com, dhaval@linux.vnet.ibm.com, Balbir Singh , skumar@linux.vnet.ibm.com Subject: Re: Regression in gdm-2.18 since 2.6.24 Message-ID: <20080405210347.GA19097@deepthought> References: <20080403191916.GA30864@deepthought> <20080404143701.GA13042@linux.vnet.ibm.com> <20080404153232.GC21753@deepthought> <20080405144042.GB24075@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20080405144042.GB24075@linux.vnet.ibm.com> User-Agent: Mutt/1.5.12-2006-07-14 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 05, 2008 at 08:10:43PM +0530, Srivatsa Vaddagiri wrote: > > Given that you seem to be seeing the problem even without > CONFIG_GROUP_SCHED, only the second hunk of the patch seems to be making > a difference for your problem i.e just the hunk below applied on > 2.6.25-rc8 (to kernel/sched_fair.c) should fix your problem too: > > @@ -1145,7 +1145,7 @@ static void check_preempt_wakeup(struct > * More easily preempt - nice tasks, while not making > * it harder for + nice tasks. > */ > - if (unlikely(se->load.weight > NICE_0_LOAD)) > + if (unlikely(se->load.weight != NICE_0_LOAD)) > gran = calc_delta_fair(gran, &se->load); > > if (pse->vruntime + gran < se->vruntime) > > [The first hunk is a no-op under !CONFIG_GROUP_SCHED, since > entity_is_task() is always 1 for !CONFIG_GROUP_SCHED] > > This second hunk changes how fast + or - niced tasks get preempted. > > 2.6.25-rc8 (Bad case): > Sets preempt granularity for + niced tasks at 5ms (1 CPU) > > 2.6.25-rc8 + the hunk above (Good case): > Sets preempt granularity for + niced tasks at >5ms > Well, I'm no longer sure exactly what was in the config, but after I had confirmed the reversion would fix 2.6.24.4 I _did_ try just the second part of the patch applied to 2.6.25-rc8 and it gave a 60% success rate across 10 tests. > > So bumping up preempt granularity for + niced tasks seems to make things > work for you. IMO the deeper problem lies somewhere else (perhaps is > some race issue in gdm itself), which is easily exposed with 2.6.25-rc8 > which lets + niced tasks be preempted quickly. > I agree this is probably exposing a problem somewhere else. > To help validate this, can you let us know the result of tuning preempt > granularity on native 2.6.25-rc8 (without any patches applied and > CONFIG_GROUP_SCHED disabled)? > > # echo 100000000 > /proc/sys/kernel/sched_wakeup_granularity_ns > > To check if echo command worked, do: > > # cat /proc/sys/kernel/sched_wakeup_granularity_ns > > It should return 100000000. > > Now try shutting down thr' gdm and pls let me know if it makes a > difference. > > -- > Regards, > vatsa Will do, but it might be a day or so before I can get to this. Thanks. Ken -- das eine Mal als Tragödie, das andere Mal als Farce