Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751376Ab3GGBbp (ORCPT ); Sat, 6 Jul 2013 21:31:45 -0400 Received: from mail-pd0-f178.google.com ([209.85.192.178]:34207 "EHLO mail-pd0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750906Ab3GGBbo (ORCPT ); Sat, 6 Jul 2013 21:31:44 -0400 Message-ID: <51D8C4F7.2010603@gmail.com> Date: Sun, 07 Jul 2013 09:31:35 +0800 From: Sam Ben User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Michael Wang CC: LKML , Ingo Molnar , Peter Zijlstra , Mike Galbraith , Alex Shi , Namhyung Kim , Paul Turner , Andrew Morton , "Nikunj A. Dadhania" , Ram Pai Subject: Re: [PATCH v3 1/2] sched: smart wake-affine foundation References: <51D50024.10902@linux.vnet.ibm.com> <51D50057.9000809@linux.vnet.ibm.com> In-Reply-To: <51D50057.9000809@linux.vnet.ibm.com> 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 Content-Length: 6460 Lines: 187 On 07/04/2013 12:55 PM, Michael Wang wrote: > wake-affine stuff is always trying to pull wakee close to waker, by theory, > this will bring benefit if waker's cpu cached hot data for wakee, or the > extreme ping-pong case. What's the meaning of ping-pong case? > > And testing show it could benefit hackbench 15% at most. > > However, the whole stuff is somewhat blindly and time-consuming, some > workload therefore suffer. > > And testing show it could damage pgbench 50% at most. > > Thus, wake-affine stuff should be more smart, and realise when to stop > it's thankless effort. > > This patch introduced 'nr_wakee_switch', which will be increased each > time the task switch it's wakee. > > So a high 'nr_wakee_switch' means the task has more than one wakee, and > bigger the number, higher the wakeup frequency. > > Now when making the decision on whether to pull or not, pay attention on > the wakee with a high 'nr_wakee_switch', pull such task may benefit wakee, > but also imply that waker will face cruel competition later, it could be > very cruel or very fast depends on the story behind 'nr_wakee_switch', > whatever, waker therefore suffer. > > Furthermore, if waker also has a high 'nr_wakee_switch', imply that multiple > tasks rely on it, then waker's higher latency will damage all of them, pull > wakee seems to be a bad deal. > > Thus, when 'waker->nr_wakee_switch / wakee->nr_wakee_switch' become higher > and higher, the deal seems to be worse and worse. > > The patch therefore help wake-affine stuff to stop it's work when: > > wakee->nr_wakee_switch > factor && > waker->nr_wakee_switch > (factor * wakee->nr_wakee_switch) > > The factor here is the node-size of current-cpu, so bigger node will lead > to more pull since the trial become more severe. > > After applied the patch, pgbench show 40% improvement at most. > > Test: > Tested with 12 cpu X86 server and tip 3.10.0-rc7. > > pgbench base smart > > | db_size | clients | tps | | tps | > +---------+---------+-------+ +-------+ > | 22 MB | 1 | 10598 | | 10796 | > | 22 MB | 2 | 21257 | | 21336 | > | 22 MB | 4 | 41386 | | 41622 | > | 22 MB | 8 | 51253 | | 57932 | > | 22 MB | 12 | 48570 | | 54000 | > | 22 MB | 16 | 46748 | | 55982 | +19.75% > | 22 MB | 24 | 44346 | | 55847 | +25.93% > | 22 MB | 32 | 43460 | | 54614 | +25.66% > | 7484 MB | 1 | 8951 | | 9193 | > | 7484 MB | 2 | 19233 | | 19240 | > | 7484 MB | 4 | 37239 | | 37302 | > | 7484 MB | 8 | 46087 | | 50018 | > | 7484 MB | 12 | 42054 | | 48763 | > | 7484 MB | 16 | 40765 | | 51633 | +26.66% > | 7484 MB | 24 | 37651 | | 52377 | +39.11% > | 7484 MB | 32 | 37056 | | 51108 | +37.92% > | 15 GB | 1 | 8845 | | 9104 | > | 15 GB | 2 | 19094 | | 19162 | > | 15 GB | 4 | 36979 | | 36983 | > | 15 GB | 8 | 46087 | | 49977 | > | 15 GB | 12 | 41901 | | 48591 | > | 15 GB | 16 | 40147 | | 50651 | +26.16% > | 15 GB | 24 | 37250 | | 52365 | +40.58% > | 15 GB | 32 | 36470 | | 50015 | +37.14% > > CC: Ingo Molnar > CC: Peter Zijlstra > CC: Mike Galbraith > Signed-off-by: Michael Wang > --- > include/linux/sched.h | 3 +++ > kernel/sched/fair.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 50 insertions(+), 0 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 178a8d9..1c996c7 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1041,6 +1041,9 @@ struct task_struct { > #ifdef CONFIG_SMP > struct llist_node wake_entry; > int on_cpu; > + struct task_struct *last_wakee; > + unsigned long nr_wakee_switch; > + unsigned long last_switch_decay; > #endif > int on_rq; > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index c61a614..a4ddbf5 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2971,6 +2971,23 @@ static unsigned long cpu_avg_load_per_task(int cpu) > return 0; > } > > +static void record_wakee(struct task_struct *p) > +{ > + /* > + * Rough decay(wiping) for cost saving, don't worry > + * about the boundary, really active task won't care > + * the loose. > + */ > + if (jiffies > current->last_switch_decay + HZ) { > + current->nr_wakee_switch = 0; > + current->last_switch_decay = jiffies; > + } > + > + if (current->last_wakee != p) { > + current->last_wakee = p; > + current->nr_wakee_switch++; > + } > +} > > static void task_waking_fair(struct task_struct *p) > { > @@ -2991,6 +3008,7 @@ static void task_waking_fair(struct task_struct *p) > #endif > > se->vruntime -= min_vruntime; > + record_wakee(p); > } > > #ifdef CONFIG_FAIR_GROUP_SCHED > @@ -3109,6 +3127,28 @@ static inline unsigned long effective_load(struct task_group *tg, int cpu, > > #endif > > +static int wake_wide(struct task_struct *p) > +{ > + int factor = nr_cpus_node(cpu_to_node(smp_processor_id())); > + > + /* > + * Yeah, it's the switching-frequency, could means many wakee or > + * rapidly switch, use factor here will just help to automatically > + * adjust the loose-degree, so bigger node will lead to more pull. > + */ > + if (p->nr_wakee_switch > factor) { > + /* > + * wakee is somewhat hot, it needs certain amount of cpu > + * resource, so if waker is far more hot, prefer to leave > + * it alone. > + */ > + if (current->nr_wakee_switch > (factor * p->nr_wakee_switch)) > + return 1; > + } > + > + return 0; > +} > + > static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > { > s64 this_load, load; > @@ -3118,6 +3158,13 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > unsigned long weight; > int balanced; > > + /* > + * If we wake multiple tasks be careful to not bounce > + * ourselves around too much. > + */ > + if (wake_wide(p)) > + return 0; > + > idx = sd->wake_idx; > this_cpu = smp_processor_id(); > prev_cpu = task_cpu(p); -- 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/