Messages in this thread | | | Date | Sun, 11 May 2008 16:10:13 +0200 (CEST) | From | Sven Wegener <> | Subject | Re: [git pull] scheduler fixes |
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On Sun, 11 May 2008, Matthew Wilcox wrote:
> On Thu, May 08, 2008 at 05:10:28PM +0200, Ingo Molnar wrote: >> @@ -258,7 +256,5 @@ static noinline void __sched __up(struct semaphore *sem) >> { >> struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list, >> struct semaphore_waiter, list); >> - list_del(&waiter->list); >> - waiter->up = 1; >> wake_up_process(waiter->task); >> } > > This might be the problem that causes the missing wakeups. If you have a > semaphore with n=2, and four processes calling down(), tasks A and B > acquire the semaphore and tasks C and D go to sleep. Task A calls up() > and wakes up C. Then task B calls up() and doesn't wake up anyone > because C hasn't run yet. I think we need another wakeup when task C > finishes in __down_common, like this (on top of your patch): > > diff --git a/kernel/semaphore.c b/kernel/semaphore.c > index 5e41217..e520ad4 100644 > --- a/kernel/semaphore.c > +++ b/kernel/semaphore.c > @@ -229,6 +229,11 @@ static inline int __sched __down_common(struct semaphore *sem, long state, > } > > list_del(&waiter.list); > + > + /* It's possible we need to wake up the next task on the list too */ > + if (unlikely(sem->count > 1) && !list_empty(&sem->wait_list)) > + __up(sem); > + > return ret; > } > > Sven, can you try this with your workload? I suspect this might be it > because XFS does use semaphores with n>1.
This one fixes the regression too, after applying it on top of bf726e.
Sven
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