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Date: Tue, 12 Oct 2010 13:24:25 +0530
From: Bharata B Rao <bharata@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: Dhaval Giani <dhaval.giani@...il.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Pavel Emelyanov <xemul@...nvz.org>,
Herbert Poetzl <herbert@...hfloor.at>,
Avi Kivity <avi@...hat.com>,
Chris Friesen <cfriesen@...tel.com>,
Paul Menage <menage@...gle.com>,
Mike Waychison <mikew@...gle.com>,
Paul Turner <pjt@...gle.com>, Nikhil Rao <ncrao@...gle.com>
Subject: [PATCH v3 6/7] sched: hierarchical task accounting for
FAIR_GROUP_SCHED
sched: hierarchical task accounting for FAIR_GROUP_SCHED
From: Paul Turner <pjt@...gle.com>
With task entities participating in throttled sub-trees it is possible for
task activation/de-activation to not lead to root visible changes to
rq->nr_running. This in turn leads to incorrect idle and weight-per-task load
balance decisions.
To allow correct accounting we move responsibility for updating rq->nr_running
to the respective sched::classes. In the fair-group case this update is
hierarchical, tracking the number of active tasks rooted at each group entity.
Note: technically this issue also exists with the existing sched_rt
throttling; however due to the nearly complete provisioning of system
resources for rt scheduling this is much less common by default.
Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
---
kernel/sched.c | 9 ++++++---
kernel/sched_fair.c | 42 ++++++++++++++++++++++++++++++++++++++++++
kernel/sched_rt.c | 5 ++++-
3 files changed, 52 insertions(+), 4 deletions(-)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -333,7 +333,7 @@ struct task_group init_task_group;
/* CFS-related fields in a runqueue */
struct cfs_rq {
struct load_weight load;
- unsigned long nr_running;
+ unsigned long nr_running, h_nr_tasks;
u64 exec_clock;
u64 min_vruntime;
@@ -1984,6 +1984,11 @@ static inline u64 sched_cfs_bandwidth_sl
#include "sched_stats.h"
+static void mod_nr_running(struct rq *rq, long delta)
+{
+ rq->nr_running += delta;
+}
+
static void inc_nr_running(struct rq *rq)
{
rq->nr_running++;
@@ -2040,7 +2045,6 @@ static void activate_task(struct rq *rq,
rq->nr_uninterruptible--;
enqueue_task(rq, p, flags);
- inc_nr_running(rq);
}
/*
@@ -2052,7 +2056,6 @@ static void deactivate_task(struct rq *r
rq->nr_uninterruptible++;
dequeue_task(rq, p, flags);
- dec_nr_running(rq);
}
#include "sched_idletask.c"
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -76,6 +76,8 @@ unsigned int sysctl_sched_child_runs_fir
*/
unsigned int __read_mostly sysctl_sched_compat_yield;
+static void account_hier_tasks(struct sched_entity *se, int delta);
+
/*
* SCHED_OTHER wake-up granularity.
* (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
@@ -683,6 +685,40 @@ account_entity_dequeue(struct cfs_rq *cf
se->on_rq = 0;
}
+#ifdef CONFIG_CFS_BANDWIDTH
+/* maintain hierarchal task counts on group entities */
+static void account_hier_tasks(struct sched_entity *se, int delta)
+{
+ struct rq *rq = rq_of(cfs_rq_of(se));
+ struct cfs_rq *cfs_rq;
+
+ for_each_sched_entity(se) {
+ /* a throttled entity cannot affect its parent hierarchy */
+ if (group_cfs_rq(se) && cfs_rq_throttled(group_cfs_rq(se)))
+ break;
+
+ /* we affect our queuing entity */
+ cfs_rq = cfs_rq_of(se);
+ cfs_rq->h_nr_tasks += delta;
+ }
+
+ /* account for global nr_running delta to hierarchy change */
+ if (!se)
+ mod_nr_running(rq, delta);
+}
+#else
+/*
+ * In the absence of group throttling, all operations are guaranteed to be
+ * globally visible at the root rq level.
+ */
+static void account_hier_tasks(struct sched_entity *se, int delta)
+{
+ struct rq *rq = rq_of(cfs_rq_of(se));
+
+ mod_nr_running(rq, delta);
+}
+#endif
+
static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHEDSTATS
@@ -1099,6 +1135,7 @@ enqueue_task_fair(struct rq *rq, struct
flags = ENQUEUE_WAKEUP;
}
+ account_hier_tasks(&p->se, 1);
hrtick_update(rq);
}
@@ -1124,6 +1161,7 @@ static void dequeue_task_fair(struct rq
flags |= DEQUEUE_SLEEP;
}
+ account_hier_tasks(&p->se, -1);
hrtick_update(rq);
}
@@ -1197,6 +1235,8 @@ static u64 tg_request_cfs_quota(struct t
return delta;
}
+static void account_hier_tasks(struct sched_entity *se, int delta);
+
static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
{
struct sched_entity *se;
@@ -1214,6 +1254,7 @@ static void throttle_cfs_rq(struct cfs_r
if (!se->on_rq)
goto out_throttled;
+ account_hier_tasks(se, -cfs_rq->h_nr_tasks);
for_each_sched_entity(se) {
struct cfs_rq *cfs_rq = cfs_rq_of(se);
@@ -1244,6 +1285,7 @@ static void unthrottle_cfs_rq(struct cfs
cfs_rq->throttled = 0;
cfs_rq->throttled_timestamp = 0;
+ account_hier_tasks(se, cfs_rq->h_nr_tasks);
for_each_sched_entity(se) {
if (se->on_rq)
break;
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -882,6 +882,8 @@ enqueue_task_rt(struct rq *rq, struct ta
if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
enqueue_pushable_task(rq, p);
+
+ inc_nr_running(rq);
}
static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
@@ -892,6 +894,8 @@ static void dequeue_task_rt(struct rq *r
dequeue_rt_entity(rt_se);
dequeue_pushable_task(rq, p);
+
+ dec_nr_running(rq);
}
/*
@@ -1754,4 +1758,3 @@ static void print_rt_stats(struct seq_fi
rcu_read_unlock();
}
#endif /* CONFIG_SCHED_DEBUG */
-
--
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