From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 2/3] sched: only run newidle if previous task was CFS Date: Tue, 24 Jun 2008 12:38:08 +0200 Message-ID: <1214303888.4351.24.camel@twins> References: <20080623225645.31515.36393.stgit@lsg.lsg.lab.novell.com> <20080623230445.31515.41728.stgit@lsg.lsg.lab.novell.com> <1214301517.4351.12.camel@twins> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: mingo@elte.hu, rostedt@goodmis.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, dbahi@novell.com To: Gregory Haskins Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:47566 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753241AbYFXKiT (ORCPT ); Tue, 24 Jun 2008 06:38:19 -0400 In-Reply-To: <1214301517.4351.12.camel@twins> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On Tue, 2008-06-24 at 11:58 +0200, Peter Zijlstra wrote: > On Mon, 2008-06-23 at 17:04 -0600, Gregory Haskins wrote: > > A system that tends to overschedule (such as PREEMPT_RT) will naturally > > tend to newidle balance often as well. This may have quite a negative > > impact on performance. This patch attempts to address the overzealous > > newidle balancing by only allowing it to occur if the previous task > > was SCHED_OTHER. > > > > Some may argue that if the system is going idle, it should try to > > newidle balance to keep it doing useful work. But the fact is that > > spending too much time in the load-balancing code demonstrably hurts > > performance as well. Running oprofile on the system with various > > workloads has shown that we can sometimes spend a majority of our > > cpu-time running load_balance_newidle. Additionally, disabling > > newidle balancing can make said workloads increase in performance by > > up to 200%. Obviously disabling the feature outright is not sustainable, > > but hopefully we can make it smarter. > > > > This code assumes that if there arent any CFS tasks present on the queue, > > it was probably already balanced. > > > > Signed-off-by: Gregory Haskins > > NAK, this wrecks idle balance for any potential other classes. > > idle_balance() is the generical hook - as can be seen from the class > iteration in move_tasks(). > > I can imagine paritioned EDF wanting to make use of these hooks to > balance the reservations. Hmm, it wouldn't,.. since its too tied in with fbg which is sched_other based,.. would need more generalization work,..