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SubjectRe: [PATCH 1/2] sched/wait: add round robin wakeup mode
On Mon, Feb 09, 2015 at 11:06:17PM -0500, Jason Baron wrote:
> On 02/09/2015 04:50 PM, Peter Zijlstra wrote:
> > On Mon, Feb 09, 2015 at 08:05:57PM +0000, Jason Baron wrote:
> >> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
> >> index 852143a..17d1039 100644
> >> --- a/kernel/sched/wait.c
> >> +++ b/kernel/sched/wait.c
> >> @@ -71,8 +71,11 @@ static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
> >> unsigned flags = curr->flags;
> >>
> >> if (curr->func(curr, mode, wake_flags, key) &&
> >> - (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
> >> + (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) {
> >> + if (flags & WQ_FLAG_ROUND_ROBIN)
> >> + list_move_tail(&curr->task_list, &q->task_list);
> >> break;
> >> + }
> >> }
> >> }
> > I think you meant to write something like:
> >
> > if (curr->func(curr, mode, wake_flags, key) &&
> > (flags & WQ_FLAG_EXCLUSIVE)) {
> > if (flag & WQ_FLAG_ROUND_ROBIN)
> > list_move_tail(&curr->task_list, &q->task_list);
> > if (!--nr_exclusive)
> > break;
> > }
> >
> > Otherwise can only work for nr_exclusive==1.
>
> Indeed. I'm also wondering if its worth avoiding the list_move_tail()
> for the case where nr_exclusive is initially 0. IE the wake all case,
> where we are just going to end up doing a bunch of list_move_tail()
> calls, but end up in the same state.

After writing this email, it occurred to me that you could probably do
this with a custom wake function.

Where autoremove_wake_function() does a list_del_init() you could do a
rotate_wake_function() that does list_move_tail().

That would avoid the entire WQ flag muckery.


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