Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753446Ab3GHCgc (ORCPT ); Sun, 7 Jul 2013 22:36:32 -0400 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:41630 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753375Ab3GHCgb (ORCPT ); Sun, 7 Jul 2013 22:36:31 -0400 Message-ID: <51DA25A4.2050803@linux.vnet.ibm.com> Date: Mon, 08 Jul 2013 10:36:20 +0800 From: Michael Wang User-Agent: Mozilla/5.0 (X11; Linux i686; rv:16.0) Gecko/20121011 Thunderbird/16.0.1 MIME-Version: 1.0 To: Sam Ben 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> <51D8C4F7.2010603@gmail.com> In-Reply-To: <51D8C4F7.2010603@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13070802-5816-0000-0000-000008CDDBC2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7454 Lines: 214 Hi, Sam On 07/07/2013 09:31 AM, Sam Ben wrote: > 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? PeterZ explained it well in here: https://lkml.org/lkml/2013/3/7/332 And you could try to compare: taskset 1 perf bench sched pipe with perf bench sched pipe to confirm it ;-) Regards, Michael Wang > >> >> 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/ > -- 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/