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SubjectRe: [PATCH 1/3] sched/rt: cpupri_find: implement fallback mechanism for !fit case
On 02/18/20 11:46, Steven Rostedt wrote:
> On Mon, 17 Feb 2020 23:45:49 +0000
> Qais Yousef <qais.yousef@arm.com> wrote:
>
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -14,6 +14,8 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);
> >
> > struct rt_bandwidth def_rt_bandwidth;
> >
> > +typedef bool (*fitness_fn_t)(struct task_struct *p, int cpu);
> > +
> > static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
> > {
> > struct rt_bandwidth *rt_b =
> > @@ -1708,6 +1710,7 @@ static int find_lowest_rq(struct task_struct *task)
> > struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
> > int this_cpu = smp_processor_id();
> > int cpu = task_cpu(task);
> > + fitness_fn_t fitness_fn;
> >
> > /* Make sure the mask is initialized first */
> > if (unlikely(!lowest_mask))
> > @@ -1716,8 +1719,17 @@ static int find_lowest_rq(struct task_struct *task)
> > if (task->nr_cpus_allowed == 1)
> > return -1; /* No other targets possible */
> >
> > + /*
> > + * Help cpupri_find avoid the cost of looking for a fitting CPU when
> > + * not really needed.
> > + */
> > + if (static_branch_unlikely(&sched_asym_cpucapacity))
> > + fitness_fn = rt_task_fits_capacity;
> > + else
> > + fitness_fn = NULL;
> > +
> > if (!cpupri_find(&task_rq(task)->rd->cpupri, task, lowest_mask,
> > - rt_task_fits_capacity))
> > + fitness_fn))
> > return -1; /* No targets found */
> >
> > /*
>
>
> If we are going to use static branches, then lets just remove the
> parameter totally. That is, make two functions (with helpers), where
> one needs this fitness function the other does not.
>
> if (static_branch_unlikely(&sched_asym_cpu_capacity))
> ret = cpupri_find_fitness(...);
> else
> ret = cpupri_find(...);
>
> if (!ret)
> return -1;
>
> Something like that?

Is there any implication on code generation here?

I like my flavour better tbh. But I don't mind refactoring the function out if
it does make it more readable.

Thanks

--
Qais Yousef

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