From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from fg-out-1718.google.com (fg-out-1718.google.com [72.14.220.152]) by ozlabs.org (Postfix) with ESMTP id 3CAD2DDE19 for ; Mon, 28 Jan 2008 20:14:38 +1100 (EST) Received: by fg-out-1718.google.com with SMTP id 16so1448088fgg.39 for ; Mon, 28 Jan 2008 01:14:37 -0800 (PST) Subject: Re: ppc32: Weird process scheduling behaviour with 2.6.24-rc From: Michel =?ISO-8859-1?Q?D=E4nzer?= To: Peter Zijlstra In-Reply-To: <1201510236.6149.24.camel@lappy> References: <1200659696.23161.81.camel@thor.sulgenrain.local> <1201013786.4726.28.camel@thor.sulgenrain.local> <1201090699.9052.39.camel@thor.sulgenrain.local> <1201092131.6341.51.camel@lappy> <1201244082.6815.128.camel@pasglop> <1201244618.6815.130.camel@pasglop> <1201245901.6815.133.camel@pasglop> <1201251000.6341.108.camel@lappy> <20080126040734.GA21365@linux.vnet.ibm.com> <1201320834.6815.160.camel@pasglop> <20080126050757.GB14177@linux.vnet.ibm.com> <1201450409.1931.23.camel@thor.sulgenrain.local> <1201510236.6149.24.camel@lappy> Content-Type: text/plain; charset=UTF-8 Date: Mon, 28 Jan 2008 10:14:33 +0100 Message-Id: <1201511673.5923.46.camel@thor.sulgenrain.local> Mime-Version: 1.0 Cc: Ingo Molnar , vatsa@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2008-01-28 at 09:50 +0100, Peter Zijlstra wrote: > On Sun, 2008-01-27 at 17:13 +0100, Michel Dänzer wrote: > > > In summary, there are two separate problems with similar symptoms, which > > had me confused at times: > > > > * With CONFIG_FAIR_USER_SCHED disabled, there are severe > > interactivity hickups with a niced CPU hog and top running. This > > started with commit 810e95ccd58d91369191aa4ecc9e6d4a10d8d0c8. > > The revert at the bottom causes the wakeup granularity to shrink for + > nice and to grow for - nice. That is, it becomes easier to preempt a + > nice task, and harder to preempt a - nice task. Yeah, that matches my observations. :) > I think we originally had that; didn't comment it, forgot the reason > changed it because the units didn't match. Another reason might have > been the more difficult preemption of - nice tasks. That might - niced > tasks to cause horrible latencies - Ingo, any recollection? > > Are you perhaps running with a very low HZ (HZ=100)? (If wakeup > preemption fails, tick preemption will take over). I haven't had it below 250 since that became an option, and I'm currently at 1000 (and NO_HZ, but disabling that didn't seem to make a difference). > Also, could you try lowering: > /proc/sys/kernel/sched_wakeup_granularity_ns Will try. > > * With CONFIG_FAIR_USER_SCHED enabled, X becomes basically > > unusable with a niced CPU hog, with or without top running. I > > don't know when this started, possibly when this option was > > first introduced. > > Srivatsa found an issue that might explain the very bad behaviour under > group scheduling. But I gather you're not at all interested in this > feature? That's right, but it's good to hear you have a lead there as well, and if you can't find any interested testers, let me know and I'll try. -- Earthling Michel Dänzer | http://tungstengraphics.com Libre software enthusiast | Debian, X and DRI developer