> That should probably look like: > > preempt_disable(); > raw_spin_unlock_irq(); > preempt_enable_no_resched(); > schedule(); > > Otherwise you might find a performance regression on PREEMPT=y kernels.
Yes, right! Thanks a lot for reminder. The following patch will fix it. > > OK, so what I was asking after is if you changed the scheduler after PJTs > patches landed to deal with this bulk wakeup. Also while aim7 might no longer > trigger the bad pattern what is to say nothing ever will? In particular > anything using pthread_cond_broadcast() is known to be suspect of bulk > wakeups. Just find a benchmark named as pthread_cond_broadcast. http://kristiannielsen.livejournal.com/13577.html. will play with it. :) > > Anyway, I'll go try and make sense of some of the actual patches.. :-) > --- >From 4c9b4b8a9b92bcbe6934637fd33c617e73dbda97 Mon Sep 17 00:00:00 2001 From: Alex Shi <alex....@intel.com> Date: Fri, 3 May 2013 14:51:25 +0800 Subject: [PATCH 8/8] rwsem: small optimizing rwsem_down_failed_common Peter Zijlstra suggest adding a preempt_enable_no_resched() to prevent a unnecessary scheduler in raw_spin_unlock. And we also can pack 2 raw_spin_lock to save one. So has this patch. Thanks Peter! Signed-off-by: Alex Shi <alex....@intel.com> --- lib/rwsem.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/lib/rwsem.c b/lib/rwsem.c index ad5e0df..9aacf81 100644 --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -212,23 +212,25 @@ rwsem_down_failed_common(struct rw_semaphore *sem, adjustment == -RWSEM_ACTIVE_WRITE_BIAS) sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED); - raw_spin_unlock_irq(&sem->wait_lock); - /* wait to be given the lock */ for (;;) { - if (!waiter.task) + if (!waiter.task) { + raw_spin_unlock_irq(&sem->wait_lock); break; + } - raw_spin_lock_irq(&sem->wait_lock); - /* Try to get the writer sem, may steal from the head writer: */ + /* Try to get the writer sem, may steal from the head writer */ if (flags == RWSEM_WAITING_FOR_WRITE) if (try_get_writer_sem(sem, &waiter)) { raw_spin_unlock_irq(&sem->wait_lock); return sem; } + preempt_disable(); raw_spin_unlock_irq(&sem->wait_lock); + preempt_enable_no_resched(); schedule(); set_task_state(tsk, TASK_UNINTERRUPTIBLE); + raw_spin_lock_irq(&sem->wait_lock); } tsk->state = TASK_RUNNING; -- 1.7.12 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
