Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755832AbYBYOQZ (ORCPT ); Mon, 25 Feb 2008 09:16:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754148AbYBYOQQ (ORCPT ); Mon, 25 Feb 2008 09:16:16 -0500 Received: from e28smtp06.in.ibm.com ([59.145.155.6]:51920 "EHLO e28esmtp06.in.ibm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754139AbYBYOQN (ORCPT ); Mon, 25 Feb 2008 09:16:13 -0500 Date: Mon, 25 Feb 2008 19:46:04 +0530 From: Dhaval Giani To: Srivatsa Vaddagiri , Ingo Molnar , Peter Zijlstra Cc: Sudhir Kumar , Balbir Singh , Aneesh Kumar KV , lkml , vgoyal@redhat.com, serue@us.ibm.com, menage@google.com Subject: [RFC, PATCH 1/2] sched: change the fairness model of the CFS group scheduler Message-ID: <20080225141604.GA29213@linux.vnet.ibm.com> Reply-To: Dhaval Giani References: <20080225141504.GA27746@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080225141504.GA27746@linux.vnet.ibm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9345 Lines: 289 This patch allows tasks and groups to exist in the same cfs_rq. With this change the CFS group scheduling follows a 1/(M+N) model from a 1/(1+N) fairness model where M tasks and N groups exist at the cfs_rq level. Signed-off-by: Dhaval Giani Signed-off-by: Srivatsa Vaddagiri --- kernel/sched.c | 46 +++++++++++++++++++++ kernel/sched_fair.c | 113 +++++++++++++++++++++++++++++++++++++++++----------- 2 files changed, 137 insertions(+), 22 deletions(-) Index: linux-2.6.25-rc2/kernel/sched.c =================================================================== --- linux-2.6.25-rc2.orig/kernel/sched.c +++ linux-2.6.25-rc2/kernel/sched.c @@ -224,10 +224,13 @@ struct task_group { }; #ifdef CONFIG_FAIR_GROUP_SCHED + +#ifdef CONFIG_USER_SCHED /* Default task group's sched entity on each cpu */ static DEFINE_PER_CPU(struct sched_entity, init_sched_entity); /* Default task group's cfs_rq on each cpu */ static DEFINE_PER_CPU(struct cfs_rq, init_cfs_rq) ____cacheline_aligned_in_smp; +#endif static struct sched_entity *init_sched_entity_p[NR_CPUS]; static struct cfs_rq *init_cfs_rq_p[NR_CPUS]; @@ -7163,6 +7166,10 @@ static void init_tg_cfs_entry(struct rq list_add(&cfs_rq->leaf_cfs_rq_list, &rq->leaf_cfs_rq_list); tg->se[cpu] = se; + /* se could be NULL for init_task_group */ + if (!se) + return; + se->cfs_rq = &rq->cfs; se->my_q = cfs_rq; se->load.weight = tg->shares; @@ -7217,11 +7224,46 @@ void __init sched_init(void) #ifdef CONFIG_FAIR_GROUP_SCHED init_task_group.shares = init_task_group_load; INIT_LIST_HEAD(&rq->leaf_cfs_rq_list); +#ifdef CONFIG_CGROUP_SCHED + /* + * How much cpu bandwidth does init_task_group get? + * + * In case of task-groups formed thr' the cgroup filesystem, it + * gets 100% of the cpu resources in the system. This overall + * system cpu resource is divided among the tasks of + * init_task_group and its child task-groups in a fair manner, + * based on each entity's (task or task-group's) weight + * (se->load.weight). + * + * In other words, if init_task_group has 10 tasks of weight + * 1024) and two child groups A0 and A1 (of weight 1024 each), + * then A0's share of the cpu resource is: + * + * A0's bandwidth = 1024 / (10*1024 + 1024 + 1024) = 8.33% + * + * We achieve this by letting init_task_group's tasks sit + * directly in rq->cfs (i.e init_task_group->se[] = NULL). + */ + init_tg_cfs_entry(rq, &init_task_group, &rq->cfs, NULL, i, 1); + init_tg_rt_entry(rq, &init_task_group, &rq->rt, NULL, i, 1); +#elif defined CONFIG_USER_SCHED + /* + * In case of task-groups formed thr' the user id of tasks, + * init_task_group represents tasks belonging to root user. + * Hence it forms a sibling of all subsequent groups formed. + * In this case, init_task_group gets only a fraction of overall + * system cpu resource, based on the weight assigned to root + * user's cpu share (INIT_TASK_GROUP_LOAD). This is accomplished + * by letting tasks of init_task_group sit in a separate cfs_rq + * (init_cfs_rq) and having one entity represent this group of + * tasks in rq->cfs (i.e init_task_group->se[] != NULL). + */ init_tg_cfs_entry(rq, &init_task_group, &per_cpu(init_cfs_rq, i), &per_cpu(init_sched_entity, i), i, 1); #endif +#endif /* CONFIG_FAIR_GROUP_SCHED */ #ifdef CONFIG_RT_GROUP_SCHED init_task_group.rt_runtime = sysctl_sched_rt_runtime * NSEC_PER_USEC; @@ -7435,6 +7477,10 @@ static int rebalance_shares(struct sched unsigned long total_load = 0, total_shares; struct task_group *tg = cfs_rq->tg; + /* Skip this group if there is no associated group entity */ + if (unlikely(!tg->se[this_cpu])) + continue; + /* Gather total task load of this group across cpus */ for_each_cpu_mask(i, sdspan) total_load += tg->cfs_rq[i]->load.weight; Index: linux-2.6.25-rc2/kernel/sched_fair.c =================================================================== --- linux-2.6.25-rc2.orig/kernel/sched_fair.c +++ linux-2.6.25-rc2/kernel/sched_fair.c @@ -732,6 +732,21 @@ static inline struct sched_entity *paren return se->parent; } +/* return the cpu load contributed by a given group on a given cpu */ +static inline unsigned long group_cpu_load(struct task_group *tg, int cpu) +{ + struct sched_entity *se = tg->se[cpu], *top_se; + struct cfs_rq *cfs_rq = tg->cfs_rq[cpu]; + + if (unlikely(!se)) + return cfs_rq->load.weight; + + for_each_sched_entity(se) + top_se = se; + + return top_se->load.weight; +} + #define GROUP_IMBALANCE_PCT 20 #else /* CONFIG_FAIR_GROUP_SCHED */ @@ -1073,6 +1088,17 @@ out_set_cpu: } #endif /* CONFIG_SMP */ +/* return depth at which a sched entity is present in the hierarchy */ +static inline int depth_se(struct sched_entity *se) +{ + int depth = 0; + + for_each_sched_entity(se) + depth++; + + return depth; +} + /* * Preempt the current task with a newly woken task if needed: @@ -1083,6 +1109,7 @@ static void check_preempt_wakeup(struct struct cfs_rq *cfs_rq = task_cfs_rq(curr); struct sched_entity *se = &curr->se, *pse = &p->se; unsigned long gran; + int se_depth, pse_depth; if (unlikely(rt_prio(p->prio))) { update_rq_clock(rq); @@ -1100,6 +1127,27 @@ static void check_preempt_wakeup(struct if (!sched_feat(WAKEUP_PREEMPT)) return; + /* + * preemption test can be made between sibling entities who are in the + * same cfs_rq i.e who have a common parent. Walk up the hierarchy of + * both tasks untill we find their ancestors who are siblings of common + * parent. + */ + + /* First walk up until both entities are at same depth */ + se_depth = depth_se(se); + pse_depth = depth_se(pse); + + while (se_depth > pse_depth) { + se_depth--; + se = parent_entity(se); + } + + while (pse_depth > se_depth) { + pse_depth--; + pse = parent_entity(pse); + } + while (!is_same_group(se, pse)) { se = parent_entity(se); pse = parent_entity(pse); @@ -1166,13 +1214,22 @@ static void put_prev_task_fair(struct rq static struct task_struct * __load_balance_iterator(struct cfs_rq *cfs_rq, struct rb_node *curr) { - struct task_struct *p; + struct task_struct *p = NULL; + struct sched_entity *se; if (!curr) return NULL; - p = rb_entry(curr, struct task_struct, se.run_node); - cfs_rq->rb_load_balance_curr = rb_next(curr); + /* Skip over entities that are not tasks */ + do { + se = rb_entry(curr, struct sched_entity, run_node); + curr = rb_next(curr); + } while (curr && !entity_is_task(se)); + + cfs_rq->rb_load_balance_curr = curr; + + if (entity_is_task(se)) + p = task_of(se); return p; } @@ -1210,21 +1267,28 @@ load_balance_fair(struct rq *this_rq, in struct cfs_rq *this_cfs_rq = busy_cfs_rq->tg->cfs_rq[this_cpu]; unsigned long maxload, task_load, group_weight; unsigned long thisload, per_task_load; - struct sched_entity *se = busy_cfs_rq->tg->se[busiest->cpu]; + struct task_group *tg = busy_cfs_rq->tg; + struct sched_entity *se = tg->se[busiest->cpu], + *this_se = tg->se[this_cpu]; task_load = busy_cfs_rq->load.weight; - group_weight = se->load.weight; + if (!task_load) + continue; + + group_weight = group_cpu_load(tg, busiest->cpu); /* - * 'group_weight' is contributed by tasks of total weight + * 'group_weight' is contributed by entities of total weight * 'task_load'. To move 'rem_load_move' worth of weight only, * we need to move a maximum task load of: * * maxload = (remload / group_weight) * task_load; */ maxload = (rem_load_move * task_load) / group_weight; + if (!maxload) + continue; - if (!maxload || !task_load) + if (!busy_cfs_rq->nr_running) continue; per_task_load = task_load / busy_cfs_rq->nr_running; @@ -1253,23 +1317,28 @@ load_balance_fair(struct rq *this_rq, in &cfs_rq_iterator); #ifdef CONFIG_FAIR_GROUP_SCHED - /* - * load_moved holds the task load that was moved. The - * effective (group) weight moved would be: - * load_moved_eff = load_moved/task_load * group_weight; - */ - load_moved = (group_weight * load_moved) / task_load; - /* Adjust shares on both cpus to reflect load_moved */ - group_weight -= load_moved; - set_se_shares(se, group_weight); + if (likely(se)) { + unsigned long load_moved_eff; + unsigned long se_shares; - se = busy_cfs_rq->tg->se[this_cpu]; - if (!thisload) - group_weight = load_moved; - else - group_weight = se->load.weight + load_moved; - set_se_shares(se, group_weight); + /* + * load_moved holds the task load that was moved. The + * effective (group) weight moved would be: + * load_moved_eff = load_moved/task_load * + * group_weight; + */ + load_moved_eff = (se->load.weight * + load_moved) / task_load; + + set_se_shares(se, se->load.weight - load_moved_eff); + if (!thisload) + se_shares = load_moved_eff; + else + se_shares = this_se->load.weight + + load_moved_eff; + set_se_shares(this_se, se_shares); + } #endif rem_load_move -= load_moved; -- regards, Dhaval -- 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/