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Message-ID: <1403684382.3462.42.camel@tkhai>
Date: Wed, 25 Jun 2014 12:19:42 +0400
From: Kirill Tkhai <ktkhai@...allels.com>
To: <linux-kernel@...r.kernel.org>
CC: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, <tkhai@...dex.ru>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
"Mike Galbraith" <umgwanakikbuti@...il.com>,
<khorenko@...allels.com>, Ben Segall <bsegall@...gle.com>,
Paul Turner <pjt@...gle.com>
Subject: [PATCH v3 1/3] sched/fair: Disable runtime_enabled on dying rq
We kill rq->rd on the CPU_DOWN_PREPARE stage:
cpuset_cpu_inactive -> cpuset_update_active_cpus -> partition_sched_domains ->
-> cpu_attach_domain -> rq_attach_root -> set_rq_offline
This unthrottles all throttled cfs_rqs.
But the cpu is still able to call schedule() till
take_cpu_down->__cpu_disable()
is called from stop_machine.
This case the tasks from just unthrottled cfs_rqs are pickable
in a standard scheduler way, and they are picked by dying cpu.
The cfs_rqs becomes throttled again, and migrate_tasks()
in migration_call skips their tasks (one more unthrottle
in migrate_tasks()->CPU_DYING does not happen, because rq->rd
is already NULL).
Patch sets runtime_enabled to zero. This guarantees, the runtime
is not accounted, and the cfs_rqs won't exceed given
cfs_rq->runtime_remaining = 1, and tasks will be pickable
in migrate_tasks(). runtime_enabled is recalculated again
when rq becomes online again.
Ben Segall also noticed, we always enable runtime in
tg_set_cfs_bandwidth(). Actually, we should do that for online
cpus only. To prevent races with unthrottle_offline_cfs_rqs()
we take get_online_cpus() lock.
v2: Fix race with tg_set_cfs_bandwidth().
Move cfs_rq->runtime_enabled=0 above unthrottle_cfs_rq().
v3: {get,put}_online_cpus()
Signed-off-by: Kirill Tkhai <ktkhai@...allels.com>
CC: Konstantin Khorenko <khorenko@...allels.com>
CC: Ben Segall <bsegall@...gle.com>
CC: Paul Turner <pjt@...gle.com>
CC: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
CC: Mike Galbraith <umgwanakikbuti@...il.com>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Ingo Molnar <mingo@...nel.org>
---
kernel/sched/core.c | 8 +++++++-
kernel/sched/fair.c | 22 ++++++++++++++++++++++
2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ceea8d0..d9c4a08 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7807,6 +7807,11 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
if (period > max_cfs_quota_period)
return -EINVAL;
+ /*
+ * Prevent race between setting of cfs_rq->runtime_enabled and
+ * unthrottle_offline_cfs_rqs().
+ */
+ get_online_cpus();
mutex_lock(&cfs_constraints_mutex);
ret = __cfs_schedulable(tg, period, quota);
if (ret)
@@ -7832,7 +7837,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
}
raw_spin_unlock_irq(&cfs_b->lock);
- for_each_possible_cpu(i) {
+ for_each_online_cpu(i) {
struct cfs_rq *cfs_rq = tg->cfs_rq[i];
struct rq *rq = cfs_rq->rq;
@@ -7848,6 +7853,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
cfs_bandwidth_usage_dec();
out_unlock:
mutex_unlock(&cfs_constraints_mutex);
+ put_online_cpus();
return ret;
}
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1f9c457..5616d23 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3776,6 +3776,19 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
hrtimer_cancel(&cfs_b->slack_timer);
}
+static void __maybe_unused update_runtime_enabled(struct rq *rq)
+{
+ struct cfs_rq *cfs_rq;
+
+ for_each_leaf_cfs_rq(rq, cfs_rq) {
+ struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;
+
+ raw_spin_lock(&cfs_b->lock);
+ cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
+ raw_spin_unlock(&cfs_b->lock);
+ }
+}
+
static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
{
struct cfs_rq *cfs_rq;
@@ -3789,6 +3802,12 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
* there's some valid quota amount
*/
cfs_rq->runtime_remaining = 1;
+ /*
+ * Offline rq is schedulable till cpu is completely disabled
+ * in take_cpu_down(), so we prevent new cfs throttling here.
+ */
+ cfs_rq->runtime_enabled = 0;
+
if (cfs_rq_throttled(cfs_rq))
unthrottle_cfs_rq(cfs_rq);
}
@@ -3832,6 +3851,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
return NULL;
}
static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
+static inline void update_runtime_enabled(struct rq *rq) {}
static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}
#endif /* CONFIG_CFS_BANDWIDTH */
@@ -7325,6 +7345,8 @@ void trigger_load_balance(struct rq *rq)
static void rq_online_fair(struct rq *rq)
{
update_sysctl();
+
+ update_runtime_enabled(rq);
}
static void rq_offline_fair(struct rq *rq)
--
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