Re: [ANNOUNCE/RFC] Really Simple Really Fair Scheduler

Ingo Molnar
2007-09-03T20:04:20Z

* Roman Zippel <zippel@linux-m68k.org> wrote:

> Hi,
>
> On Mon, 3 Sep 2007, Ingo Molnar wrote:
>
> > My next question then is about this code of yours in the wakeup path:
> >
> > +static void
> > +enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
> > +{
> > + kclock_t min_time;
> > +
> > + verify_queue(cfs_rq, cfs_rq->curr != se, se);
> > + min_time = get_time_avg(cfs_rq) - se->req_weight_inv;
> > + if ((kclock_t)(se->time_norm - min_time) < 0)
> > + se->time_norm = min_time;
> >
> > why do you only use the "min_time" if the pre-sleep time_norm is smaller
> > than the min_time? Here 'min_time' is close to the current average.
>
> It's a variation of the sleeper bonus. [...]

hm, where are its effects described in your explanation? Seems like a
key item.

> [...] Let's assume two running tasks which have been running for 95ms
> and 105ms and a time slice of 10ms, the average is thus 100ms. If the
> new task has been sleeping for a while it starts at 90ms, if the task
> had been running lately it doesn't get this bonus again.

what happens if there are lots of such tasks? What limits the total
bonus?

> > Shouldnt here the woken up task be set to the average time, like i
> > did it in the crude prototype:
> >
> > + se->exec_runtime = avg_exec_runtime(cfs_rq);
>
> That would be equivalent to simply clearing wait_runtime in CFS.

so my prototype patch is not an exact map of the nice-0 special-case of
your code? Would this be the correct thing then perhaps:

+ se->exec_runtime =
+ max(avg_exec_runtime(cfs_rq), se->exec_runtime);

Or if not, could you suggest a code-line at that place? Thanks,

Ingo