Messages in this thread | | | Date | Tue, 07 May 2013 15:51:14 +0800 | From | Alex Shi <> | Subject | Re: [PATCH v4 0/6] sched: use runnable load based balance |
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On 05/03/2013 03:55 PM, Alex Shi wrote: > >> 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. >>
Peter, would you like to pick this patch? > > --- > > From 4c9b4b8a9b92bcbe6934637fd33c617e73dbda97 Mon Sep 17 00:00:00 2001 > From: Alex Shi <alex.shi@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.shi@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; >
-- Thanks Alex
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