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SubjectRe: [PATCH 3/3] sched/fair: fix unnecessary increase of balance interval
On Thu, 13 Dec 2018 at 14:52, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Aug 07, 2018 at 05:56:27PM +0200, Vincent Guittot wrote:
> > +static inline bool
> > +asym_active_balance(enum cpu_idle_type idle, unsigned int flags, int dst, int src)
> > {
> > + if (idle != CPU_NOT_IDLE) {
> >
> > /*
> > * ASYM_PACKING needs to force migrate tasks from busy but
> > * lower priority CPUs in order to pack all tasks in the
> > * highest priority CPUs.
> > */
> > + if ((flags & SD_ASYM_PACKING) &&
> > + sched_asym_prefer(dst, src))
> > + return true;
> > }
> >
> > + return false;
> > +}
> > +
> > +static int need_active_balance(struct lb_env *env)
> > +{
> > + struct sched_domain *sd = env->sd;
> > +
> > +
> > + if (asym_active_balance(env->idle, sd->flags, env->dst_cpu, env->src_cpu))
> > + return 1;
> > +
> > /*
> > * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
> > * It's worth migrating the task if the src_cpu's capacity is reduced
> > @@ -8650,7 +8660,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
> > } else
> > sd->nr_balance_failed = 0;
> >
> > + if (likely(!active_balance) ||
> > + asym_active_balance(env.idle, sd->flags, env.dst_cpu, env.src_cpu)) {
>
> Perhaps like the below?

Yes. Far more simple and readable

>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8857,21 +8857,24 @@ static struct rq *find_busiest_queue(str
> */
> #define MAX_PINNED_INTERVAL 512
>
> +static inline bool
> +asym_active_balance(struct lb_env *env)
> +{
> + /*
> + * ASYM_PACKING needs to force migrate tasks from busy but
> + * lower priority CPUs in order to pack all tasks in the
> + * highest priority CPUs.
> + */
> + return env->idle != CPU_NOT_IDLE && (env->sd->flags & SD_ASYM_PACKING) &&
> + sched_asym_prefer(env->dst_cpu, env->src_cpu);
> +}
> +
> static int need_active_balance(struct lb_env *env)
> {
> struct sched_domain *sd = env->sd;
>
> - if (env->idle != CPU_NOT_IDLE) {
> -
> - /*
> - * ASYM_PACKING needs to force migrate tasks from busy but
> - * lower priority CPUs in order to pack all tasks in the
> - * highest priority CPUs.
> - */
> - if ((sd->flags & SD_ASYM_PACKING) &&
> - sched_asym_prefer(env->dst_cpu, env->src_cpu))
> - return 1;
> - }
> + if (asym_active_balance(env))
> + return 1;
>
> /*
> * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
> @@ -9150,7 +9153,7 @@ static int load_balance(int this_cpu, st
> } else
> sd->nr_balance_failed = 0;
>
> - if (likely(!active_balance)) {
> + if (likely(!active_balance) || asym_active_balance(&env)) {
> /* We were unbalanced, so reset the balancing interval */
> sd->balance_interval = sd->min_interval;
> } else {

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