Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753359Ab3HBEZ3 (ORCPT ); Fri, 2 Aug 2013 00:25:29 -0400 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:52943 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750853Ab3HBEZ2 (ORCPT ); Fri, 2 Aug 2013 00:25:28 -0400 Message-ID: <51FB341B.7060104@linux.vnet.ibm.com> Date: Fri, 02 Aug 2013 09:52:51 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Joonsoo Kim CC: Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, Mike Galbraith , Paul Turner , Alex Shi , Vincent Guittot , Morten Rasmussen , Namhyung Kim , Joonsoo Kim Subject: Re: [PATCH v2 2/3] sched: factor out code to should_we_balance() References: <1375408223-10934-1-git-send-email-iamjoonsoo.kim@lge.com> <1375408223-10934-3-git-send-email-iamjoonsoo.kim@lge.com> In-Reply-To: <1375408223-10934-3-git-send-email-iamjoonsoo.kim@lge.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: 13080204-2000-0000-0000-00000D247347 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5817 Lines: 166 Hi Joonsoo, On 08/02/2013 07:20 AM, Joonsoo Kim wrote: > Now checking whether this cpu is appropriate to balance or not > is embedded into update_sg_lb_stats() and this checking has no direct > relationship to this function. There is not enough reason to place > this checking at update_sg_lb_stats(), except saving one iteration > for sched_group_cpus. > > In this patch, I factor out this checking to should_we_balance() function. > And before doing actual work for load_balancing, check whether this cpu is > appropriate to balance via should_we_balance(). If this cpu is not > a candidate for balancing, it quit the work immediately. > > With this change, we can save two memset cost and can expect better > compiler optimization. > > Below is result of this patch. > > * Vanilla * > text data bss dec hex filename > 34499 1136 116 35751 8ba7 kernel/sched/fair.o > > * Patched * > text data bss dec hex filename > 34243 1136 116 35495 8aa7 kernel/sched/fair.o > > In addition, rename @balance to @should_balance in order to represent > its purpose more clearly. > > Signed-off-by: Joonsoo Kim > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index eaae77e..7f51b8c 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4426,22 +4426,17 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group) > * @group: sched_group whose statistics are to be updated. > * @load_idx: Load index of sched_domain of this_cpu for load calc. > * @local_group: Does group contain this_cpu. > - * @balance: Should we balance. > * @sgs: variable to hold the statistics for this group. > */ > static inline void update_sg_lb_stats(struct lb_env *env, > struct sched_group *group, int load_idx, > - int local_group, int *balance, struct sg_lb_stats *sgs) > + int local_group, struct sg_lb_stats *sgs) > { > unsigned long nr_running, max_nr_running, min_nr_running; > unsigned long load, max_cpu_load, min_cpu_load; > - unsigned int balance_cpu = -1, first_idle_cpu = 0; > unsigned long avg_load_per_task = 0; > int i; > > - if (local_group) > - balance_cpu = group_balance_cpu(group); > - > /* Tally up the load of all CPUs in the group */ > max_cpu_load = 0; > min_cpu_load = ~0UL; > @@ -4454,15 +4449,9 @@ 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) { > - if (idle_cpu(i) && !first_idle_cpu && > - cpumask_test_cpu(i, sched_group_mask(group))) { > - first_idle_cpu = 1; > - balance_cpu = i; > - } > - > + if (local_group) > load = target_load(i, load_idx); > - } else { > + else { > load = source_load(i, load_idx); > if (load > max_cpu_load) > max_cpu_load = load; > @@ -4482,22 +4471,9 @@ static inline void update_sg_lb_stats(struct lb_env *env, > sgs->idle_cpus++; > } > > - /* > - * First idle cpu or the first cpu(busiest) in this sched group > - * is eligible for doing load balancing at this and above > - * domains. In the newly idle case, we will allow all the cpu's > - * to do the newly idle load balance. > - */ > - if (local_group) { > - if (env->idle != CPU_NEWLY_IDLE) { > - if (balance_cpu != env->dst_cpu) { > - *balance = 0; > - return; > - } > - update_group_power(env->sd, env->dst_cpu); > - } else if (time_after_eq(jiffies, group->sgp->next_update)) > - update_group_power(env->sd, env->dst_cpu); > - } Observe what is happening in the above code which checks if we should balance on the env->dst_cpu. Only if the env->dst_cpu "belongs" to the group considered in update_sg_lb_stats(), which means local_group = 1,should the above checks be carried out. Meaning, if there is a better CPU in the same group to which env->dst_cpu belongs, to carry out load balancing for the system (in the above case, balance_cpu), cancel the current iteration of load balancing on env->dst_cpu. Wait for the right cpu in this group to do the load balancing. Keeping this in mind see the below comments around should_we_balance(). > @@ -5001,13 +4964,47 @@ static int need_active_balance(struct lb_env *env) > > static int active_load_balance_cpu_stop(void *data); > > +static int should_we_balance(struct lb_env *env) > +{ > + struct sched_group *sg = env->sd->groups; > + struct cpumask *sg_cpus, *sg_mask; > + int cpu, balance_cpu = -1; > + > + /* > + * In the newly idle case, we will allow all the cpu's > + * to do the newly idle load balance. > + */ > + if (env->idle == CPU_NEWLY_IDLE) > + return 1; > + > + sg_cpus = sched_group_cpus(sg); > + sg_mask = sched_group_mask(sg); > + /* Try to find first idle cpu */ > + for_each_cpu_and(cpu, sg_cpus, env->cpus) { > + if (!cpumask_test_cpu(cpu, sg_mask) || idle_cpu(cpu)) > + continue; > + > + balance_cpu = cpu; > + break; > + } You need to iterate over all the groups of the sched domain env->sd and not just the first group of env->sd like you are doing above. This is to check to which group the env->dst_cpu belongs to. Only for that group should you do the above check and set of balance_cpu and the below check of balance_cpu != env->dst_cpu. > + > + if (balance_cpu == -1) > + balance_cpu = group_balance_cpu(sg); > + > + /* > + * First idle cpu or the first cpu(busiest) in this sched group > + * is eligible for doing load balancing at this and above domains. > + */ > + return balance_cpu != env->dst_cpu; Regards Preeti U Murthy -- 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/