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Message-ID: <20080225141604.GA29213@linux.vnet.ibm.com>
Date: Mon, 25 Feb 2008 19:46:04 +0530
From: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
Balbir Singh <balbir@...ibm.com>,
Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
lkml <linux-kernel@...r.kernel.org>, vgoyal@...hat.com,
serue@...ibm.com, menage@...gle.com
Subject: [RFC, PATCH 1/2] sched: change the fairness model of the CFS group
scheduler
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 <dhaval@...ux.vnet.ibm.com>
Signed-off-by: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
---
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
--
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