Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754221AbYLOIZd (ORCPT ); Mon, 15 Dec 2008 03:25:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752283AbYLOIZY (ORCPT ); Mon, 15 Dec 2008 03:25:24 -0500 Received: from viefep14-int.chello.at ([62.179.121.34]:1424 "EHLO viefep18-int.chello.at" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752266AbYLOIZY (ORCPT ); Mon, 15 Dec 2008 03:25:24 -0500 X-SourceIP: 213.46.9.244 Subject: Re: [RFC PATCH v5 4/7] sched: bias task wakeups to preferred semi-idle packages From: Peter Zijlstra To: balbir@linux.vnet.ibm.com Cc: Vaidyanathan Srinivasan , Linux Kernel , Suresh B Siddha , Venkatesh Pallipadi , Ingo Molnar , Dipankar Sarma , Vatsa , Gautham R Shenoy , Andi Kleen , David Collier-Brown , Tim Connors , Max Krasnyansky , Gregory Haskins In-Reply-To: <20081215070139.GE18403@balbir.in.ibm.com> References: <20081211173831.2020.57550.stgit@drishya.in.ibm.com> <20081211174304.2020.14746.stgit@drishya.in.ibm.com> <20081215070139.GE18403@balbir.in.ibm.com> Content-Type: text/plain Date: Mon, 15 Dec 2008 09:25:21 +0100 Message-Id: <1229329521.14605.17.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2011 Lines: 56 On Mon, 2008-12-15 at 12:31 +0530, Balbir Singh wrote: > > kernel/sched_fair.c | 17 +++++++++++++++++ > > 1 files changed, 17 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > > index 98345e4..939f2a1 100644 > > --- a/kernel/sched_fair.c > > +++ b/kernel/sched_fair.c > > @@ -1027,6 +1027,23 @@ static int wake_idle(int cpu, struct task_struct *p) > > cpumask_t tmp; > > struct sched_domain *sd; > > int i; > > + unsigned int chosen_wakeup_cpu; > > + int this_cpu; > > + > > + /* > > + * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu > > + * are idle and this is not a kernel thread and this task's affinity > > + * allows it to be moved to preferred cpu, then just move! > > + */ > > + > > + this_cpu = smp_processor_id(); > > + chosen_wakeup_cpu = > > + cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu; > > + > > + if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP && > > + idle_cpu(cpu) && idle_cpu(this_cpu) && p->mm && > > The p->mm check is racy, it needs to be done under task_lock(). The > best way to check for a kernel thread is get_task_mm(), followed by > put_task_mm() is the mm is not NULL. We also need to check to see if > the task is _hot_ on cpu. We should negate this optimization in case > chosen_wakeup_cpu is idle, so check for that as well. Sure its racy, but so what? The worst I can see it that we exclude a dying task from this logic, which isn't a problem at all, since its dying anyway. Also, I don't think you can grab task_lock() from under rq->lock... > > + cpu_isset(chosen_wakeup_cpu, p->cpus_allowed)) > > + return chosen_wakeup_cpu; > > > > /* > > * If it is idle, then it is the best cpu to run this task. > > > > > -- 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/