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Date: Sat, 27 Feb 2010 15:41:52 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [GIT PULL] scheduler fixes for v2.6.34
Linus,
Please pull the latest sched-fixes-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git sched-fixes-for-linus
These are the pending fixes queued up after v2.6.33-rc8.
Thanks,
Ingo
------------------>
Andrew Morton (1):
kernel/sched.c: Suppress unused var warning
Peter Zijlstra (1):
sched: Fix race between ttwu() and task_rq_lock()
Suresh Siddha (1):
sched: Fix SMT scheduler regression in find_busiest_queue()
Vaidyanathan Srinivasan (1):
sched: Fix sched_mv_power_savings for !SMT
include/linux/sched.h | 5 ++-
kernel/sched.c | 86 +++++++++++++++++++++++++++++++++----------------
2 files changed, 62 insertions(+), 29 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 78efe7c..1f5fa53 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -878,7 +878,10 @@ static inline int sd_balance_for_mc_power(void)
if (sched_smt_power_savings)
return SD_POWERSAVINGS_BALANCE;
- return SD_PREFER_SIBLING;
+ if (!sched_mc_power_savings)
+ return SD_PREFER_SIBLING;
+
+ return 0;
}
static inline int sd_balance_for_package_power(void)
diff --git a/kernel/sched.c b/kernel/sched.c
index 3a8fb30..404e201 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -941,16 +941,33 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
#endif /* __ARCH_WANT_UNLOCKED_CTXSW */
/*
+ * Check whether the task is waking, we use this to synchronize against
+ * ttwu() so that task_cpu() reports a stable number.
+ *
+ * We need to make an exception for PF_STARTING tasks because the fork
+ * path might require task_rq_lock() to work, eg. it can call
+ * set_cpus_allowed_ptr() from the cpuset clone_ns code.
+ */
+static inline int task_is_waking(struct task_struct *p)
+{
+ return unlikely((p->state == TASK_WAKING) && !(p->flags & PF_STARTING));
+}
+
+/*
* __task_rq_lock - lock the runqueue a given task resides on.
* Must be called interrupts disabled.
*/
static inline struct rq *__task_rq_lock(struct task_struct *p)
__acquires(rq->lock)
{
+ struct rq *rq;
+
for (;;) {
- struct rq *rq = task_rq(p);
+ while (task_is_waking(p))
+ cpu_relax();
+ rq = task_rq(p);
raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p)))
+ if (likely(rq == task_rq(p) && !task_is_waking(p)))
return rq;
raw_spin_unlock(&rq->lock);
}
@@ -967,10 +984,12 @@ static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
struct rq *rq;
for (;;) {
+ while (task_is_waking(p))
+ cpu_relax();
local_irq_save(*flags);
rq = task_rq(p);
raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p)))
+ if (likely(rq == task_rq(p) && !task_is_waking(p)))
return rq;
raw_spin_unlock_irqrestore(&rq->lock, *flags);
}
@@ -2408,14 +2427,27 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
__task_rq_unlock(rq);
cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
- if (cpu != orig_cpu)
+ if (cpu != orig_cpu) {
+ /*
+ * Since we migrate the task without holding any rq->lock,
+ * we need to be careful with task_rq_lock(), since that
+ * might end up locking an invalid rq.
+ */
set_task_cpu(p, cpu);
+ }
- rq = __task_rq_lock(p);
+ rq = cpu_rq(cpu);
+ raw_spin_lock(&rq->lock);
update_rq_clock(rq);
+ /*
+ * We migrated the task without holding either rq->lock, however
+ * since the task is not on the task list itself, nobody else
+ * will try and migrate the task, hence the rq should match the
+ * cpu we just moved it to.
+ */
+ WARN_ON(task_cpu(p) != cpu);
WARN_ON(p->state != TASK_WAKING);
- cpu = task_cpu(p);
#ifdef CONFIG_SCHEDSTATS
schedstat_inc(rq, ttwu_count);
@@ -2663,7 +2695,13 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
set_task_cpu(p, cpu);
#endif
- rq = task_rq_lock(p, &flags);
+ /*
+ * Since the task is not on the rq and we still have TASK_WAKING set
+ * nobody else will migrate this task.
+ */
+ rq = cpu_rq(cpu);
+ raw_spin_lock_irqsave(&rq->lock, flags);
+
BUG_ON(p->state != TASK_WAKING);
p->state = TASK_RUNNING;
update_rq_clock(rq);
@@ -4119,12 +4157,23 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
continue;
rq = cpu_rq(i);
- wl = weighted_cpuload(i) * SCHED_LOAD_SCALE;
- wl /= power;
+ wl = weighted_cpuload(i);
+ /*
+ * When comparing with imbalance, use weighted_cpuload()
+ * which is not scaled with the cpu power.
+ */
if (capacity && rq->nr_running == 1 && wl > imbalance)
continue;
+ /*
+ * For the load comparisons with the other cpu's, consider
+ * the weighted_cpuload() scaled with the cpu power, so that
+ * the load can be moved away from the cpu that is potentially
+ * running at a lower capacity.
+ */
+ wl = (wl * SCHED_LOAD_SCALE) / power;
+
if (wl > max_load) {
max_load = wl;
busiest = rq;
@@ -7145,27 +7194,8 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
struct rq *rq;
int ret = 0;
- /*
- * Since we rely on wake-ups to migrate sleeping tasks, don't change
- * the ->cpus_allowed mask from under waking tasks, which would be
- * possible when we change rq->lock in ttwu(), so synchronize against
- * TASK_WAKING to avoid that.
- *
- * Make an exception for freshly cloned tasks, since cpuset namespaces
- * might move the task about, we have to validate the target in
- * wake_up_new_task() anyway since the cpu might have gone away.
- */
-again:
- while (p->state == TASK_WAKING && !(p->flags & PF_STARTING))
- cpu_relax();
-
rq = task_rq_lock(p, &flags);
- if (p->state == TASK_WAKING && !(p->flags & PF_STARTING)) {
- task_rq_unlock(rq, &flags);
- goto again;
- }
-
if (!cpumask_intersects(new_mask, cpu_active_mask)) {
ret = -EINVAL;
goto out;
--
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