diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2015-10-16 14:39:38 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-12-04 10:33:41 +0100 |
| commit | b3e0b1b6d841a4b2f64fc09ea728913da8218424 (patch) | |
| tree | 93df412814210f3e4d36dae4e39487aec17a431e /kernel | |
| parent | 829cf31751aa1c50b1527c1e0c821c99246b5639 (diff) | |
locking, sched: Introduce smp_cond_acquire() and use it
Introduce smp_cond_acquire() which combines a control dependency and a
read barrier to form acquire semantics.
This primitive has two benefits:
- it documents control dependencies,
- its typically cheaper than using smp_load_acquire() in a loop.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/locking/qspinlock.c | 3 | ||||
| -rw-r--r-- | kernel/sched/core.c | 8 | ||||
| -rw-r--r-- | kernel/sched/sched.h | 2 |
3 files changed, 3 insertions, 10 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 986207887def..ed9d96708f93 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -433,8 +433,7 @@ queue: * */ pv_wait_head(lock, node); - while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_PENDING_MASK) - cpu_relax(); + smp_cond_acquire(!((val = atomic_read(&lock->val)) & _Q_LOCKED_PENDING_MASK)); /* * claim the lock: diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 7063c6a07440..9f7862da2cd1 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1968,19 +1968,13 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) /* * If the owning (remote) cpu is still in the middle of schedule() with * this task as prev, wait until its done referencing the task. - */ - while (p->on_cpu) - cpu_relax(); - /* - * Combined with the control dependency above, we have an effective - * smp_load_acquire() without the need for full barriers. * * Pairs with the smp_store_release() in finish_lock_switch(). * * This ensures that tasks getting woken will be fully ordered against * their previous state and preserve Program Order. */ - smp_rmb(); + smp_cond_acquire(!p->on_cpu); p->sched_contributes_to_load = !!task_contributes_to_load(p); p->state = TASK_WAKING; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index b242775bf670..1e0bb4afe3fd 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1076,7 +1076,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev) * In particular, the load of prev->state in finish_task_switch() must * happen before this. * - * Pairs with the control dependency and rmb in try_to_wake_up(). + * Pairs with the smp_cond_acquire() in try_to_wake_up(). */ smp_store_release(&prev->on_cpu, 0); #endif |