Re: Question: RT schedular : task_tick_rt(struct rq *rq, structtask_struct *p) : decreases overhead when rq->nr_running == 1

Re: Question: RT schedular : task_tick_rt(struct rq *rq, structtask_struct *p) : decreases overhead when rq->nr_running == 1

[Mitchell Erblich]

Ingo Molnar and group,

First, RT/RR tasks are not deprecated.  This
change simply removes sched overhead while
only 1 RT/RR task is runable per rq.

The code size increase is minor and is a very
straightforward change..

THUS...

    My assumption is / was to hand you/Ingo Molnar this change
    because,
        * you have the latest scheduler git tree and do periodic
           pull requests, so I consider you the default scheduler
           maintainer ....   : ^ )
        * my scheduler tree is more developmental,
        * and I wish to first suggest minor changes over time to see
           what scheduler changes are more acceptable.

  Mitchell Erblich
----------------------


Ingo Molnar wrote:
>
> * Mitchell Erblich <erblichs@earthlink.net> wrote:
>
> > After
> >     p->time_slice = static_prio_timeslice(p->static_prio);
> >
> > Why isn't their a check like
> >     if  (rq->nr_running == 1)
> >          return;
> >
> > Which world remove the need for any recheduling or requeue'ing...
>
> your change is a possible optimization, but this is a pretty rare
> codepath because the overwhelming majority of RT apps uses SCHED_FIFO.
> Plus, the time_slice going down to 0 is a relatively rare event even for
> SCHED_RR tasks. And if we have only a single SCHED_RR task, why is it
> SCHED_RR to begin with? So this is on several levels an uncommon
> workload and by adding a check like that we'd increase the codesize. But
> ... no strong feelings against this optimization - if you send a proper
> patch we can apply it, it certainly makes sense from a logic POV.
>
>         Ingo
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Re: Question: RT schedular : task_tick_rt(struct rq *rq, structtask_struct *p) : decreases overhead when rq->nr_running == 1

[Ingo Molnar]

* Mitchell Erblich <erblichs@earthlink.net> wrote:

> First, RT/RR tasks are not deprecated. [...]

I'm confused, do you say this in reference to anything i said? I did not 
say that RR tasks are deprecated and you were top-posting so i cannot 
connect it to anything specific. I only said RR tasks are _rare_:

>> this is a pretty rare codepath because the overwhelming majority of 
>> RT apps uses SCHED_FIFO [...]

and i hope you can see the difference between 'rare' and 'deprecated' 
;-) And i suspect you also missed the last bit of what i wrote:

>> So this is on several levels an uncommon workload and by adding a 
>> check like that we'd increase the codesize. But ... no strong 
>> feelings against this optimization - if you send a proper patch we 
>> can apply it, it certainly makes sense from a logic POV.

and you also missed the first bit it appears:

>> your change is a possible optimization, [...]

so you are banging, with full force, on completely open doors =B-)

	Ingo