Jonathan
On Tue, 11 May 1999, Ingo Molnar wrote:
> On Tue, 11 May 1999, Andrea Arcangeli wrote:
> > >> 1) there are no idle cpu in the system
> > >> 2) the prev task was in general the less priority one
> > >
> > >wrong. We actively _preempt_ processes on other CPUs, this means that a
> >
> > If I understand well the only wrong thing I said is point (2). But if you
> > would read better my email I stated clearly that point (2) it not the pure
> > reality, but instead I said that it's a very good approximation of the
> > pure reality.
> >
> > >preempted process has all rights to try to replace even lesser priority
> > >processes on other CPUs. Your problem might be that you are thinking in
> >
> > You should rereadd my previous email. I never said it's useless, I have
> > said that it's not worthwile.
>
> it is always 'worthwile' to have a correct scheduler. This was the sole
> purpose of all the 2.2.8 scheduler changes!
>
> > You mean that a preemted process has all rights to preempt a even lesser
> > priority CPU. But ask you _why_ such process is been preempted. Simply
> > because in general we can see it as the _less_ priority one.
>
> not necesserily, it might as well just be replaced by a RT process ...
>
> > I repeat that as global design I prefer to have such call in schedule_tail
> > even if according to me it's only a performance _hit_.
>
> it is not a performance hit at all because most processes reschedule
> 'voluntarily', ie. they get removed from the runqueue.
>
> There is one inconsistency left though, if the previous process was
> SCHED_YIELD then we should obviously not push it to other CPUs, because it
> has just given up it's timeslice. (the attached untested patch fixes this)
>
> -- mingo
>
> --- linux/kernel/sched.c.orig Tue May 11 13:29:39 1999
> +++ linux/kernel/sched.c Tue May 11 13:38:32 1999
> @@ -194,10 +194,8 @@
> static inline int prev_goodness (struct task_struct * prev,
> struct task_struct * p, int this_cpu)
> {
> - if (p->policy & SCHED_YIELD) {
> - p->policy &= ~SCHED_YIELD;
> + if (p->policy & SCHED_YIELD)
> return 0;
> - }
> return goodness(prev, p, this_cpu);
> }
>
> @@ -659,10 +657,16 @@
> */
> static inline void __schedule_tail (struct task_struct *prev)
> {
> + if (prev->policy & SCHED_YIELD)
> + prev->policy &= ~SCHED_YIELD;
> + else {
> +#ifdef __SMP__
> + if ((prev->state == TASK_RUNNING) &&
> + (prev != idle_task(smp_processor_id())))
> + reschedule_idle(prev);
> +#endif
> + }
> #ifdef __SMP__
> - if ((prev->state == TASK_RUNNING) &&
> - (prev != idle_task(smp_processor_id())))
> - reschedule_idle(prev);
> wmb();
> prev->has_cpu = 0;
> #endif /* __SMP__ */
>
>
> -
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