Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754116Ab3GJBwa (ORCPT ); Tue, 9 Jul 2013 21:52:30 -0400 Received: from mail-yh0-f53.google.com ([209.85.213.53]:43973 "EHLO mail-yh0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754024Ab3GJBw2 (ORCPT ); Tue, 9 Jul 2013 21:52:28 -0400 Message-ID: <51DCBE49.9000806@gmail.com> Date: Wed, 10 Jul 2013 09:52:09 +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> <51D8C4F7.2010603@gmail.com> <51DA25A4.2050803@linux.vnet.ibm.com> In-Reply-To: <51DA25A4.2050803@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: 7786 Lines: 213 On 07/08/2013 10:36 AM, Michael Wang wrote: > 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 Why sched pipe is special? > > 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/