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Re: [RFC][PATCH 3/8] sched/deadline/rtmutex: Dont miss the dl_runtime/dl_period update

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  Re: [RFC][PATCH 3/8] sched/deadline/rtmutex: Dont miss the  dl_runtime/dl_period update Juri Lelli <juri.lelli@arm.com> - 2016-06-14 12:50 +0200
    Re: [RFC][PATCH 3/8] sched/deadline/rtmutex: Dont miss the  dl_runtime/dl_period update Peter Zijlstra <peterz@infradead.org> - 2016-06-14 14:10 +0200

#1421763 — Re: [RFC][PATCH 3/8] sched/deadline/rtmutex: Dont miss the dl_runtime/dl_period update

Hi,

On 07/06/16 21:56, Peter Zijlstra wrote:
> From: Xunlei Pang <xlpang@redhat.com>
> 
> Currently dl tasks will actually return at the very beginning
> of rt_mutex_adjust_prio_chain() in !detect_deadlock cases:
> 
>     if (waiter->prio == task->prio) {
>         if (!detect_deadlock)
>             goto out_unlock_pi; // out here
>         else
>             requeue = false;
>     }
> 
> As the deadline value of blocked deadline tasks(waiters) without
> changing their sched_class(thus prio doesn't change) never changes,
> this seems reasonable, but it actually misses the chance of updating
> rt_mutex_waiter's "dl_runtime(period)_copy" if a waiter updates its
> deadline parameters(dl_runtime, dl_period) or boosted waiter changes
> to !deadline class.
> 
> Thus, force deadline task not out by adding the !dl_prio() condition.
> 
> [peterz: I should introduce more task state comparators like
> rt_mutex_waiter_less, all PI prio comparisons already have this DL
> exception, except this one]
> 
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Juri Lelli <juri.lelli@arm.com>
> Signed-off-by: Xunlei Pang <xlpang@redhat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: http://lkml.kernel.org/r/1460633827-345-7-git-send-email-xlpang@redhat.com
> ---
>  kernel/locking/rtmutex.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -488,7 +488,7 @@ static int rt_mutex_adjust_prio_chain(st
>  	 * enabled we continue, but stop the requeueing in the chain
>  	 * walk.
>  	 */
> -	if (waiter->prio == task->prio) {
> +	if (waiter->prio == task->prio && !dl_task(task)) {

Right. Do we want a rt_mutex_waiter_equal() helper? As I think the
comment in the changelog was also saying?

Best,

- Juri

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#1421848

On Tue, Jun 14, 2016 at 11:43:39AM +0100, Juri Lelli wrote:
> > [peterz: I should introduce more task state comparators like
> > rt_mutex_waiter_less, all PI prio comparisons already have this DL
> > exception, except this one]

> > +++ b/kernel/locking/rtmutex.c
> > @@ -488,7 +488,7 @@ static int rt_mutex_adjust_prio_chain(st
> >  	 * enabled we continue, but stop the requeueing in the chain
> >  	 * walk.
> >  	 */
> > -	if (waiter->prio == task->prio) {
> > +	if (waiter->prio == task->prio && !dl_task(task)) {
> 
> Right. Do we want a rt_mutex_waiter_equal() helper? As I think the
> comment in the changelog was also saying?

rt_mutex_waiter_equal() isn't going to help; it will not work on code
that doesn't have access to rt_mutex_waiter thingies, like
rt_mutex_setprio() for example. 

Then again, I already wondered about making rt_mutex_waiter available to
sched code, but tglx didn't much like that iirc.

Esp. given the last patch in this series, I wondered if perhaps the
second argument to rt_mutex_setprio() should be a struct
rt_mutex_waiter, instead of struct task_struct.

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