From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755595Ab3LSNe0 (ORCPT ); Thu, 19 Dec 2013 08:34:26 -0500 Received: from mail-pb0-f48.google.com ([209.85.160.48]:61188 "EHLO mail-pb0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755496Ab3LSNeX (ORCPT ); Thu, 19 Dec 2013 08:34:23 -0500 Message-ID: <52B2F5D0.2050707@linaro.org> Date: Thu, 19 Dec 2013 21:34:08 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Peter Zijlstra , Morten Rasmussen CC: "mingo@redhat.com" , "vincent.guittot@linaro.org" , "daniel.lezcano@linaro.org" , "fweisbec@gmail.com" , "linux@arm.linux.org.uk" , "tony.luck@intel.com" , "fenghua.yu@intel.com" , "tglx@linutronix.de" , "akpm@linux-foundation.org" , "arjan@linux.intel.com" , "pjt@google.com" , "fengguang.wu@intel.com" , "james.hogan@imgtec.com" , "jason.low2@hp.com" , "gregkh@linuxfoundation.org" , "hanjun.guo@linaro.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 4/4] sched: bias to target cpu load to reduce task moving References: <1386061556-28233-1-git-send-email-alex.shi@linaro.org> <1386061556-28233-5-git-send-email-alex.shi@linaro.org> <20131217141012.GG10134@e103034-lin> <20131217153809.GP21999@twins.programming.kicks-ass.net> In-Reply-To: <20131217153809.GP21999@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/17/2013 11:38 PM, Peter Zijlstra wrote: > On Tue, Dec 17, 2013 at 02:10:12PM +0000, Morten Rasmussen wrote: >>> @@ -4135,7 +4141,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu) >>> if (local_group) >>> load = source_load(i); >>> else >>> - load = target_load(i); >>> + load = target_load(i, sd->imbalance_pct); >> >> Don't you apply imbalance_pct twice here? Later on in >> find_idlest_group() you have: >> >> if (!idlest || 100*this_load < imbalance*min_load) >> return NULL; >> >> where min_load comes from target_load(). > > Yes! exactly! this doesn't make any sense. Thanks a lot for review and comments! I changed the patch to following shape. and push it under Fengguang's testing system monitor. Any testing are appreciated! BTW, Seems lots of changes in scheduler come from kinds of scenarios/benchmarks experience. But I still like to take any theoretical comments/suggestions. -- Thanks Alex === >>From 5cd67d975001edafe2ee820e0be5d86881a23bd6 Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Sat, 23 Nov 2013 23:18:09 +0800 Subject: [PATCH 4/4] sched: bias to target cpu load to reduce task moving Task migration happens when target just a bit less then source cpu load. To reduce such situation happens, aggravate the target cpu load with sd->imbalance_pct/100 in wake_affine. In find_idlest/busiest_group, change the aggravate to local cpu only from old group aggravation. on my pandaboard ES. latest kernel 527d1511310a89 + whole patchset hackbench -T -g 10 -f 40 23.25" 21.99" 23.16" 21.20" 24.24" 21.89" hackbench -p -g 10 -f 40 26.52" 21.46" 23.89" 22.96" 25.65" 22.73" hackbench -P -g 10 -f 40 20.14" 19.72" 19.96" 19.10" 21.76" 20.03" Signed-off-by: Alex Shi --- kernel/sched/fair.c | 35 ++++++++++++++++------------------- 1 file changed, 16 insertions(+), 19 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bccdd89..3623ba4 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -978,7 +978,7 @@ static inline unsigned long group_weight(struct task_struct *p, int nid) static unsigned long weighted_cpuload(const int cpu); static unsigned long source_load(int cpu); -static unsigned long target_load(int cpu); +static unsigned long target_load(int cpu, int imbalance_pct); static unsigned long power_of(int cpu); static long effective_load(struct task_group *tg, int cpu, long wl, long wg); @@ -3809,11 +3809,17 @@ static unsigned long source_load(int cpu) * Return a high guess at the load of a migration-target cpu weighted * according to the scheduling class and "nice" value. */ -static unsigned long target_load(int cpu) +static unsigned long target_load(int cpu, int imbalance_pct) { struct rq *rq = cpu_rq(cpu); unsigned long total = weighted_cpuload(cpu); + /* + * without cpu_load decay, in most of time cpu_load is same as total + * so we need to make target a bit heavier to reduce task migration + */ + total = total * imbalance_pct / 100; + if (!sched_feat(LB_BIAS)) return total; @@ -4033,7 +4039,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) this_cpu = smp_processor_id(); prev_cpu = task_cpu(p); load = source_load(prev_cpu); - this_load = target_load(this_cpu); + this_load = target_load(this_cpu, 100); /* * If sync wakeup then subtract the (maximum possible) @@ -4089,7 +4095,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) if (balanced || (this_load <= load && - this_load + target_load(prev_cpu) <= tl_per_task)) { + this_load + target_load(prev_cpu, 100) <= tl_per_task)) { /* * This domain has SD_WAKE_AFFINE and * p is cache cold in this domain, and @@ -4112,7 +4118,6 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu) { struct sched_group *idlest = NULL, *group = sd->groups; unsigned long min_load = ULONG_MAX, this_load = 0; - int imbalance = 100 + (sd->imbalance_pct-100)/2; do { unsigned long load, avg_load; @@ -4132,10 +4137,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu) for_each_cpu(i, sched_group_cpus(group)) { /* Bias balancing toward cpus of our domain */ - if (local_group) + if (i == this_cpu) load = source_load(i); else - load = target_load(i); + load = target_load(i, sd->imbalance_pct); avg_load += load; } @@ -4151,7 +4156,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu) } } while (group = group->next, group != sd->groups); - if (!idlest || 100*this_load < imbalance*min_load) + if (!idlest || this_load < min_load) return NULL; return idlest; } @@ -5476,9 +5481,9 @@ static inline void update_sg_lb_stats(struct lb_env *env, nr_running = rq->nr_running; - /* Bias balancing toward cpus of our domain */ - if (local_group) - load = target_load(i); + /* Bias balancing toward dst cpu */ + if (env->dst_cpu == i) + load = target_load(i, env->sd->imbalance_pct); else load = source_load(i); @@ -5918,14 +5923,6 @@ static struct sched_group *find_busiest_group(struct lb_env *env) if ((local->idle_cpus < busiest->idle_cpus) && busiest->sum_nr_running <= busiest->group_weight) goto out_balanced; - } else { - /* - * In the CPU_NEWLY_IDLE, CPU_NOT_IDLE cases, use - * imbalance_pct to be conservative. - */ - if (100 * busiest->avg_load <= - env->sd->imbalance_pct * local->avg_load) - goto out_balanced; } force_balance: -- 1.8.1.2