From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752833AbZHZSxD (ORCPT ); Wed, 26 Aug 2009 14:53:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752586AbZHZSxC (ORCPT ); Wed, 26 Aug 2009 14:53:02 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:34439 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750846AbZHZSxA (ORCPT ); Wed, 26 Aug 2009 14:53:00 -0400 Message-ID: <4A958480.3070207@us.ibm.com> Date: Wed, 26 Aug 2009 11:52:48 -0700 From: Darren Hart User-Agent: Thunderbird 2.0.0.23 (X11/20090817) MIME-Version: 1.0 To: Peter Zijlstra CC: Thomas Gleixner , Ingo Molnar , linux-kernel Subject: Re: [RFC][PATCH -rt] sched: fully ignore RT tasks for CFS load-balancing References: <1251297875.18584.5.camel@twins> In-Reply-To: <1251297875.18584.5.camel@twins> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: > Since -rt runs IRQs and SoftIRQs as RT tasks and load-balancing is done > from softirq context, there is always at least one RT task (and very > likely multiple) running when we balance. > > The current (and totally broken) interaction between RT tasks and CFS > load-balancing makes it so that we'll try to evacuate a significant > amount of tasks due to RT tasks being runnable. > > Solve this in another broken way by not accounting RT tasks at all. > > This will likely break another class of cases, but until we can properly > fix this, we might as well do this. Peter, Do we know why this became a problem lately? I don't recall seeing load balancing issues like this way back around 2.6.21 or 22 when CFS was released. Is the cpu_load stuff fairly recent? -- Darren > > Chucked-on-by: Peter Zijlstra > --- > kernel/sched_rt.c | 4 ---- > 1 files changed, 0 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c > index adcbc68..385d31f 100644 > --- a/kernel/sched_rt.c > +++ b/kernel/sched_rt.c > @@ -926,8 +926,6 @@ static void enqueue_task_rt(struct rq *rq, struct > task_struct *p, int wakeup) > > if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1) > enqueue_pushable_task(rq, p); > - > - inc_cpu_load(rq, p->se.load.weight); > } > > static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int > sleep) > @@ -942,8 +940,6 @@ static void dequeue_task_rt(struct rq *rq, struct > task_struct *p, int sleep) > dequeue_rt_entity(rt_se); > > dequeue_pushable_task(rq, p); > - > - dec_cpu_load(rq, p->se.load.weight); > } > > /* > > -- > 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/ > -- Darren Hart IBM Linux Technology Center Real-Time Linux Team