[tip:sched/core] sched: Add TASK_WAKING

tip-bot for Peter Zijlstra
2009-09-16T10:21:03Z

Commit-ID: e9c8431185d6c406887190519f6dbdd112641686
Gitweb: http://git.kernel.org/tip/e9c8431185d6c406887190519f6dbdd112641686
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Tue, 15 Sep 2009 14:43:03 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 15 Sep 2009 16:01:05 +0200

sched: Add TASK_WAKING

We're going to want to drop rq->lock in try_to_wake_up() for a
longer period of time, however we also want to deal with concurrent
waking of the same task, which is currently handled by holding
rq->lock.

So introduce a new TASK state, namely TASK_WAKING, which indicates
someone is already waking the task (other wakers will fail p->state
& state).

We also keep preemption disabled over the whole ttwu().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
include/linux/sched.h | 1 +
kernel/sched.c | 31 +++++++++++++++----------------
2 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5d3c990..3b0ca66 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -190,6 +190,7 @@ extern unsigned long long time_sync_thresh;
/* in tsk->state again */
#define TASK_DEAD 64
#define TASK_WAKEKILL 128
+#define TASK_WAKING 256

/* Convenience macros for the sake of set_task_state */
#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
diff --git a/kernel/sched.c b/kernel/sched.c
index 32b7a81..fc6fda8 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2310,7 +2310,6 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
{
int cpu, orig_cpu, this_cpu, success = 0;
unsigned long flags;
- long old_state;
struct rq *rq;

if (!sched_feat(SYNC_WAKEUPS))
@@ -2332,11 +2331,12 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
}
#endif

+ this_cpu = get_cpu();
+
smp_wmb();
rq = task_rq_lock(p, &flags);
update_rq_clock(rq);
- old_state = p->state;
- if (!(old_state & state))
+ if (!(p->state & state))
goto out;

if (p->se.on_rq)
@@ -2344,27 +2344,25 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)

cpu = task_cpu(p);
orig_cpu = cpu;
- this_cpu = smp_processor_id();

#ifdef CONFIG_SMP
if (unlikely(task_running(rq, p)))
goto out_activate;

+ /*
+ * In order to handle concurrent wakeups and release the rq->lock
+ * we put the task in TASK_WAKING state.
+ */
+ p->state = TASK_WAKING;
+ task_rq_unlock(rq, &flags);
+
cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, sync);
- if (cpu != orig_cpu) {
+ if (cpu != orig_cpu)
set_task_cpu(p, cpu);
- task_rq_unlock(rq, &flags);
- /* might preempt at this point */
- rq = task_rq_lock(p, &flags);
- old_state = p->state;
- if (!(old_state & state))
- goto out;
- if (p->se.on_rq)
- goto out_running;

- this_cpu = smp_processor_id();
- cpu = task_cpu(p);
- }
+ rq = task_rq_lock(p, &flags);
+ WARN_ON(p->state != TASK_WAKING);
+ cpu = task_cpu(p);

#ifdef CONFIG_SCHEDSTATS
schedstat_inc(rq, ttwu_count);
@@ -2422,6 +2420,7 @@ out_running:
#endif
out:
task_rq_unlock(rq, &flags);
+ put_cpu();

return success;
}