Messages in this thread | | | Subject | Re: [RFC] Patch: dynticks: idle load balancing | From | Steven Rostedt <> | Date | Tue, 19 Dec 2006 19:49:03 -0500 |
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On Mon, 2006-12-11 at 15:53 -0800, Siddha, Suresh B wrote:
> > Comments and review feedback welcome. Minimal testing done on couple of > i386 platforms. Perf testing yet to be done.
Nice work!
> > thanks, > suresh > ---
> diff -pNru linux-2.6.19-mm1/include/linux/sched.h linux/include/linux/sched.h > --- linux-2.6.19-mm1/include/linux/sched.h 2006-12-12 06:39:22.000000000 -0800 > +++ linux/include/linux/sched.h 2006-12-12 06:51:03.000000000 -0800 > @@ -195,6 +195,14 @@ extern void sched_init_smp(void); > extern void init_idle(struct task_struct *idle, int cpu); > > extern cpumask_t nohz_cpu_mask; > +#ifdef CONFIG_SMP > +extern int select_notick_load_balancer(int cpu); > +#else > +static inline int select_notick_load_balancer(int cpu)
Later on in the actual code, the parameter is named stop_tick, which makes sense. You should change the name here too so it's not confusing when looking later on at the code.
> +{ > + return 0; > +} > +#endif
[...]
> + > +/* > + * This routine will try to nominate the ilb (idle load balancing) > + * owner among the cpus whose ticks are stopped. ilb owner will do the idle > + * load balancing on behalf of all those cpus. If all the cpus in the system > + * go into this tickless mode, then there will be no ilb owner (as there is > + * no need for one) and all the cpus will sleep till the next wakeup event > + * arrives... > + * > + * For the ilb owner, tick is not stopped. And this tick will be used > + * for idle load balancing. ilb owner will still be part of > + * notick.cpu_mask.. > + * > + * While stopping the tick, this cpu will become the ilb owner if there > + * is no other owner. And will be the owner till that cpu becomes busy > + * or if all cpus in the system stop their ticks at which point > + * there is no need for ilb owner. > + * > + * When the ilb owner becomes busy, it nominates another owner, during the > + * schedule() > + */ > +int select_notick_load_balancer(int stop_tick) > +{ > + int cpu = smp_processor_id(); > +
[...]
> +#ifdef CONFIG_NO_HZ > + if (idle_cpu(local_cpu) && notick.load_balancer == local_cpu && > + !cpus_empty(cpus)) > + goto restart; > +#endif > } > #else > /* > @@ -3562,6 +3669,21 @@ switch_tasks: > ++*switch_count; > > prepare_task_switch(rq, next); > +#if defined(CONFIG_HZ) && defined(CONFIG_SMP)
Ah! so this is where the CONFIG_NO_HZ mistake came in ;)
> + if (prev == rq->idle && notick.load_balancer == -1) { > + /* > + * simple selection for now: Nominate the first cpu in > + * the notick list to be the next ilb owner. > + * > + * TBD: Traverse the sched domains and nominate > + * the nearest cpu in the notick.cpu_mask. > + */ > + int ilb = first_cpu(notick.cpu_mask); > + > + if (ilb != NR_CPUS) > + resched_cpu(ilb); > + } > +#endif > prev = context_switch(rq, prev, next);
-- Steve
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