Re: [git pull] scheduler fixes

Matthew Wilcox
2008-05-11T13:02:52Z

On Sun, May 11, 2008 at 02:52:16PM +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
>
> > > So I deem my fix "proven by thought experiment". I haven't tried
> > > booting it or anything.
> >
> > i actually have two fixes, made earlier today. The 'fix3' one has been
> > confirmed by Sven to fix the regression - but i think we need the 'fix
> > #2' one below as well to make it complete.
>
> i just combined them into a single fix, see below.

That's mangled ... why did you move __up around?

> list_del(&waiter.list);
> + if (unlikely(!list_empty(&sem->wait_list)) && sem->count)
> + __up(sem);

That's an unnecessary wakeup compared to my patch.

> return ret;
> }
>
> @@ -254,9 +264,10 @@ static noinline int __sched __down_timeo
> return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies);
> }
>
> -static noinline void __sched __up(struct semaphore *sem)
> -{
> - struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
> - struct semaphore_waiter, list);
> - wake_up_process(waiter->task);
> -}
> +
> + /*
> + * Rotate sleepers - to make sure all of them get woken in case
> + * of parallel up()s:
> + */
> + list_move_tail(&waiter->list, &sem->wait_list);

Seems like extra cache line dirtying for no real gain over my solution.

--
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