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SubjectRe: [PATCH 2/3] sched: enforce per-cpu utilization limits on runtime balancing
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Thu, Feb 25, 2010 09:28:23PM +0100
>
> On Tue, 2010-02-23 at 19:56 +0100, Fabio Checconi wrote:
> > +#ifdef CONFIG_SMP
> > +static inline unsigned long rt_init_free_bw(void)
> > +{
> > + unsigned long used = to_ratio(global_rt_period(), global_rt_runtime());
> > +
> > + return to_ratio(RUNTIME_INF, RUNTIME_INF) - used;
> > +}
> > +#endif
>
> > +static void __rt_restart_balancing(void)
> > +{
> > + unsigned long used, global, free;
> > + struct rq *rq;
> > + int i;
> > +
> > + used = rt_used_bandwidth();
> > + global = to_ratio(RUNTIME_INF, RUNTIME_INF);
> > +
> > + free = global - used;
>
>
> We take the max as RUNTIME_INF instead of global_rt_* so that we can
> move runtime around and fully saturate a single cpu (given there is
> enough free to compensate on other cpus) ?

The only reason I've used RUNTIME_INF instead of global_rt_* is for the
!GROUP_SCHED case, where using the global_rt_* values would make balancing
have no effect at all (the initial value for def_rt_bandwidth already
uses the maximum bw on each cpu) . The current throttling implementation
in this case still tries to concentrate bw on a single cpu, and I wanted
to replicate the same behaviour.

Should I go for the global_rt_* values and add some #ifdef unreadability
to avoid the balancing overhead in the !GROUP_SCHED case?


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