Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753996AbYLOHEh (ORCPT ); Mon, 15 Dec 2008 02:04:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753251AbYLOHE0 (ORCPT ); Mon, 15 Dec 2008 02:04:26 -0500 Received: from E23SMTP04.au.ibm.com ([202.81.18.173]:52317 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751788AbYLOHEZ (ORCPT ); Mon, 15 Dec 2008 02:04:25 -0500 Date: Mon, 15 Dec 2008 12:31:39 +0530 From: Balbir Singh To: Vaidyanathan Srinivasan Cc: Linux Kernel , Suresh B Siddha , Venkatesh Pallipadi , Peter Zijlstra , Ingo Molnar , Dipankar Sarma , Vatsa , Gautham R Shenoy , Andi Kleen , David Collier-Brown , Tim Connors , Max Krasnyansky , Gregory Haskins Subject: Re: [RFC PATCH v5 4/7] sched: bias task wakeups to preferred semi-idle packages Message-ID: <20081215070139.GE18403@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com Mail-Followup-To: Vaidyanathan Srinivasan , Linux Kernel , Suresh B Siddha , Venkatesh Pallipadi , Peter Zijlstra , Ingo Molnar , Dipankar Sarma , Vatsa , Gautham R Shenoy , Andi Kleen , David Collier-Brown , Tim Connors , Max Krasnyansky , Gregory Haskins References: <20081211173831.2020.57550.stgit@drishya.in.ibm.com> <20081211174304.2020.14746.stgit@drishya.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20081211174304.2020.14746.stgit@drishya.in.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3113 Lines: 81 * Vaidyanathan Srinivasan [2008-12-11 23:13:04]: > Preferred wakeup cpu (from a semi idle package) has been > nominated in find_busiest_group() in the previous patch. Use > this information in sched_mc_preferred_wakeup_cpu in function > wake_idle() to bias task wakeups if the following conditions > are satisfied: > - The present cpu that is trying to wakeup the process is > idle and waking the target process on this cpu will > potentially wakeup a completely idle package > - The previous cpu on which the target process ran is > also idle and hence selecting the previous cpu may > wakeup a semi idle cpu package > - The task being woken up is allowed to run in the > nominated cpu (cpu affinity and restrictions) > > Basically if both the current cpu and the previous cpu on > which the task ran is idle, select the nominated cpu from semi > idle cpu package for running the new task that is waking up. > > Cache hotness is considered since the actual biasing happens > in wake_idle() only if the application is cache cold. > > This technique will effectively move short running bursty jobs in > a mostly idle system. > > Wakeup biasing for power savings gets automatically disabled if > system utilisation increases due to the fact that the probability > of finding both this_cpu and prev_cpu idle decreases. > > Signed-off-by: Vaidyanathan Srinivasan > --- > > 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. > + 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. > > -- Balbir -- 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/