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Date: Mon, 13 Jan 2014 07:55:18 -0800
From: tip-bot for Peter Zijlstra <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
peterz@...radead.org, tglx@...utronix.de
Subject: [tip:sched/core] sched/deadline: Fix hotplug admission control
Commit-ID: de212f18e92c952533d57c5510d2790199c75734
Gitweb: http://git.kernel.org/tip/de212f18e92c952533d57c5510d2790199c75734
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 19 Dec 2013 11:54:45 +0100
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 13 Jan 2014 13:47:25 +0100
sched/deadline: Fix hotplug admission control
The current hotplug admission control is broken because:
CPU_DYING -> migration_call() -> migrate_tasks() -> __migrate_task()
cannot fail and hard assumes it _will_ move all tasks off of the dying
cpu, failing this will break hotplug.
The much simpler solution is a DOWN_PREPARE handler that fails when
removing one CPU gets us below the total allocated bandwidth.
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/20131220171343.GL2480@laptop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
kernel/sched/core.c | 83 +++++++++++++++++++++--------------------------------
1 file changed, 32 insertions(+), 51 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1d33eb8..a549d9a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1887,9 +1887,15 @@ inline struct dl_bw *dl_bw_of(int i)
return &cpu_rq(i)->rd->dl_bw;
}
-static inline int __dl_span_weight(struct rq *rq)
+static inline int dl_bw_cpus(int i)
{
- return cpumask_weight(rq->rd->span);
+ struct root_domain *rd = cpu_rq(i)->rd;
+ int cpus = 0;
+
+ for_each_cpu_and(i, rd->span, cpu_active_mask)
+ cpus++;
+
+ return cpus;
}
#else
inline struct dl_bw *dl_bw_of(int i)
@@ -1897,7 +1903,7 @@ inline struct dl_bw *dl_bw_of(int i)
return &cpu_rq(i)->dl.dl_bw;
}
-static inline int __dl_span_weight(struct rq *rq)
+static inline int dl_bw_cpus(int i)
{
return 1;
}
@@ -1938,8 +1944,7 @@ static int dl_overflow(struct task_struct *p, int policy,
u64 period = attr->sched_period;
u64 runtime = attr->sched_runtime;
u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0;
- int cpus = __dl_span_weight(task_rq(p));
- int err = -1;
+ int cpus, err = -1;
if (new_bw == p->dl.dl_bw)
return 0;
@@ -1950,6 +1955,7 @@ static int dl_overflow(struct task_struct *p, int policy,
* allocated bandwidth of the container.
*/
raw_spin_lock(&dl_b->lock);
+ cpus = dl_bw_cpus(task_cpu(p));
if (dl_policy(policy) && !task_has_dl_policy(p) &&
!__dl_overflow(dl_b, cpus, 0, new_bw)) {
__dl_add(dl_b, new_bw);
@@ -4522,42 +4528,6 @@ out:
EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
/*
- * When dealing with a -deadline task, we have to check if moving it to
- * a new CPU is possible or not. In fact, this is only true iff there
- * is enough bandwidth available on such CPU, otherwise we want the
- * whole migration procedure to fail over.
- */
-static inline
-bool set_task_cpu_dl(struct task_struct *p, unsigned int cpu)
-{
- struct dl_bw *dl_b = dl_bw_of(task_cpu(p));
- struct dl_bw *cpu_b = dl_bw_of(cpu);
- int ret = 1;
- u64 bw;
-
- if (dl_b == cpu_b)
- return 1;
-
- raw_spin_lock(&dl_b->lock);
- raw_spin_lock(&cpu_b->lock);
-
- bw = cpu_b->bw * cpumask_weight(cpu_rq(cpu)->rd->span);
- if (dl_bandwidth_enabled() &&
- bw < cpu_b->total_bw + p->dl.dl_bw) {
- ret = 0;
- goto unlock;
- }
- dl_b->total_bw -= p->dl.dl_bw;
- cpu_b->total_bw += p->dl.dl_bw;
-
-unlock:
- raw_spin_unlock(&cpu_b->lock);
- raw_spin_unlock(&dl_b->lock);
-
- return ret;
-}
-
-/*
* Move (not current) task off this cpu, onto dest cpu. We're doing
* this because either it can't run here any more (set_cpus_allowed()
* away from this CPU, or CPU going down), or because we're
@@ -4589,13 +4559,6 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
goto fail;
/*
- * If p is -deadline, proceed only if there is enough
- * bandwidth available on dest_cpu
- */
- if (unlikely(dl_task(p)) && !set_task_cpu_dl(p, dest_cpu))
- goto fail;
-
- /*
* If we're not on a rq, the next wake-up will ensure we're
* placed properly.
*/
@@ -5052,13 +5015,31 @@ static int sched_cpu_active(struct notifier_block *nfb,
static int sched_cpu_inactive(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
+ unsigned long flags;
+ long cpu = (long)hcpu;
+
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_DOWN_PREPARE:
- set_cpu_active((long)hcpu, false);
+ set_cpu_active(cpu, false);
+
+ /* explicitly allow suspend */
+ if (!(action & CPU_TASKS_FROZEN)) {
+ struct dl_bw *dl_b = dl_bw_of(cpu);
+ bool overflow;
+ int cpus;
+
+ raw_spin_lock_irqsave(&dl_b->lock, flags);
+ cpus = dl_bw_cpus(cpu);
+ overflow = __dl_overflow(dl_b, cpus, 0, 0);
+ raw_spin_unlock_irqrestore(&dl_b->lock, flags);
+
+ if (overflow)
+ return notifier_from_errno(-EBUSY);
+ }
return NOTIFY_OK;
- default:
- return NOTIFY_DONE;
}
+
+ return NOTIFY_DONE;
}
static int __init migration_init(void)
--
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