Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753491AbYLOIdg (ORCPT ); Mon, 15 Dec 2008 03:33:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752532AbYLOId0 (ORCPT ); Mon, 15 Dec 2008 03:33:26 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:39160 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752316AbYLOId0 (ORCPT ); Mon, 15 Dec 2008 03:33:26 -0500 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: <1229329521.14605.17.camel@twins> References: <20081211173831.2020.57550.stgit@drishya.in.ibm.com> <20081211174304.2020.14746.stgit@drishya.in.ibm.com> <20081215070139.GE18403@balbir.in.ibm.com> <1229329521.14605.17.camel@twins> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Mon, 15 Dec 2008 09:33:04 +0100 Message-Id: <1229329984.14605.18.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2231 Lines: 58 On Mon, 2008-12-15 at 09:25 +0100, Peter Zijlstra wrote: > 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. At which point I seriously doubt it'd still be on the rq 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/