From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752960Ab0JMTKU (ORCPT ); Wed, 13 Oct 2010 15:10:20 -0400 Received: from smtp-out.google.com ([74.125.121.35]:11592 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752894Ab0JMTKS (ORCPT ); Wed, 13 Oct 2010 15:10:18 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=from:to:cc:subject:date:message-id:x-mailer:in-reply-to:references; b=lQIop5pTEyo2acEgtbEhx9zT8xUwxsRS2tCKIrx75/wXMm1f4sxR49lYbRB5vBoKZ IqDavf08/G+AEHVOk6SdQ== From: Nikhil Rao To: Ingo Molnar , Peter Zijlstra , Mike Galbraith , Suresh Siddha , Venkatesh Pallipadi Cc: linux-kernel@vger.kernel.org, Nikhil Rao Subject: [PATCH 4/4] sched: force balancing on newidle balance if local group has capacity Date: Wed, 13 Oct 2010 12:09:38 -0700 Message-Id: <1286996978-7007-5-git-send-email-ncrao@google.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1286996978-7007-1-git-send-email-ncrao@google.com> References: <1286996978-7007-1-git-send-email-ncrao@google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch forces a load balance on a newly idle cpu when the local group has extra capacity and the busiest group does not have any. It improves system utilization when balancing tasks with a large weight differential. Under certain situations, such as a niced down task (i.e. nice = -15) in the presence of nr_cpus NICE0 tasks, the niced task lands on a sched group and kicks away other tasks because of its large weight. This leads to sub-optimal utilization of the machine. Even though the sched group has capacity, it does not pull tasks because sds.this_load >> sds.max_load, and f_b_g() returns NULL. With this patch, if the local group has extra capacity, we shortcut the checks in f_b_g() and try to pull a task over. A sched group has extra capacity if the group capacity is greater than the number of running tasks in that group. Thanks to Mike Galbraith for discussions leading to this patch and for the insight to reuse SD_NEWIDLE_BALANCE. Signed-off-by: Nikhil Rao --- kernel/sched_fair.c | 30 +++++++++++++++++++++++++++--- 1 files changed, 27 insertions(+), 3 deletions(-) diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 2f38b8a..202fa25 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1764,6 +1764,10 @@ static void pull_task(struct rq *src_rq, struct task_struct *p, set_task_cpu(p, this_cpu); activate_task(this_rq, p, 0); check_preempt_curr(this_rq, p, 0); + + /* re-arm NEWIDLE balancing when moving tasks */ + src_rq->avg_idle = this_rq->avg_idle = 2*sysctl_sched_migration_cost; + this_rq->idle_stamp = 0; } /* @@ -2031,12 +2035,14 @@ struct sd_lb_stats { unsigned long this_load_per_task; unsigned long this_nr_running; unsigned long this_group_capacity; + unsigned long this_has_capacity; /* Statistics of the busiest group */ unsigned long max_load; unsigned long busiest_load_per_task; unsigned long busiest_nr_running; unsigned long busiest_group_capacity; + unsigned long busiest_has_capacity; int group_imb; /* Is there imbalance in this sd */ #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT) @@ -2059,6 +2065,7 @@ struct sg_lb_stats { unsigned long sum_weighted_load; /* Weighted load of group's tasks */ unsigned long group_capacity; int group_imb; /* Is there an imbalance in the group ? */ + int group_has_capacity; /* Is there extra capacity in the group? */ }; /** @@ -2459,6 +2466,9 @@ static inline void update_sg_lb_stats(struct sched_domain *sd, DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE); if (!sgs->group_capacity) sgs->group_capacity = fix_small_capacity(sd, group); + + if (sgs->group_capacity > sgs->sum_nr_running) + sgs->group_has_capacity = 1; } /** @@ -2560,12 +2570,14 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu, sds->this_nr_running = sgs.sum_nr_running; sds->this_group_capacity = sgs.group_capacity; sds->this_load_per_task = sgs.sum_weighted_load; + sds->this_has_capacity = sgs.group_has_capacity; } else if (update_sd_pick_busiest(sd, sds, sg, &sgs, this_cpu)) { sds->max_load = sgs.avg_load; sds->busiest = sg; sds->busiest_nr_running = sgs.sum_nr_running; sds->busiest_group_capacity = sgs.group_capacity; sds->busiest_load_per_task = sgs.sum_weighted_load; + sds->busiest_has_capacity = sgs.group_has_capacity; sds->group_imb = sgs.group_imb; } @@ -2762,6 +2774,15 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu, return fix_small_imbalance(sds, this_cpu, imbalance); } + +bool check_utilization(struct sd_lb_stats *sds) +{ + if (!sds->this_has_capacity || sds->busiest_has_capacity) + return false; + + return true; +} + /******* find_busiest_group() helpers end here *********************/ /** @@ -2824,6 +2845,10 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, if (!sds.busiest || sds.busiest_nr_running == 0) goto out_balanced; + /* SD_BALANCE_NEWIDLE trumps SMP nice when underutilized */ + if (idle == CPU_NEWLY_IDLE && check_utilization(&sds)) + goto force_balance; + if (sds.this_load >= sds.max_load) goto out_balanced; @@ -2835,6 +2860,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load) goto out_balanced; +force_balance: /* Looks like there is an imbalance. Compute it */ calculate_imbalance(&sds, this_cpu, imbalance); return sds.busiest; @@ -3161,10 +3187,8 @@ static void idle_balance(int this_cpu, struct rq *this_rq) interval = msecs_to_jiffies(sd->balance_interval); if (time_after(next_balance, sd->last_balance + interval)) next_balance = sd->last_balance + interval; - if (pulled_task) { - this_rq->idle_stamp = 0; + if (pulled_task) break; - } } raw_spin_lock(&this_rq->lock); -- 1.7.1