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    SubjectRe: [PATCH 7/7] sched/uclamp: Cater for uclamp in find_energy_efficient_cpu()'s early exit condition
    On 07/20/22 15:39, Xuewen Yan wrote:
    > Hi Qais
    >
    > On Thu, Jun 30, 2022 at 3:48 AM Qais Yousef <qais.yousef@arm.com> wrote:
    > >
    > > If the utilization of the woken up task is 0, we skip the energy
    > > calculation because it has no impact.
    > >
    > > But if the task is boosted (uclamp_min != 0) will have an impact on task
    > > placement and frequency selection. Only skip if the util is truly
    > > 0 after applying uclamp values.
    > >
    > > Change uclamp_task_cpu() signature to avoid unnecessary additional calls
    > > to uclamp_eff_get(). feec() is the only user now.
    > >
    > > Fixes: 732cd75b8c920 ("sched/fair: Select an energy-efficient CPU on task wake-up")
    > > Signed-off-by: Qais Yousef <qais.yousef@arm.com>
    > > ---
    > > kernel/sched/fair.c | 14 ++++++++------
    > > 1 file changed, 8 insertions(+), 6 deletions(-)
    > >
    > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > > index 499ef7a7288c..a112ca45864c 100644
    > > --- a/kernel/sched/fair.c
    > > +++ b/kernel/sched/fair.c
    > > @@ -4057,14 +4057,16 @@ static inline unsigned long task_util_est(struct task_struct *p)
    > > }
    > >
    > > #ifdef CONFIG_UCLAMP_TASK
    > > -static inline unsigned long uclamp_task_util(struct task_struct *p)
    > > +static inline unsigned long uclamp_task_util(struct task_struct *p,
    > > + unsigned long uclamp_min,
    > > + unsigned long uclamp_max)
    > > {
    > > - return clamp(task_util_est(p),
    > > - uclamp_eff_value(p, UCLAMP_MIN),
    > > - uclamp_eff_value(p, UCLAMP_MAX));
    > > + return clamp(task_util_est(p), uclamp_min, uclamp_max);
    > > }
    > > #else
    > > -static inline unsigned long uclamp_task_util(struct task_struct *p)
    > > +static inline unsigned long uclamp_task_util(struct task_struct *p,
    > > + unsigned long uclamp_min,
    > > + unsigned long uclamp_max)
    > > {
    > > return task_util_est(p);
    > > }
    > > @@ -6913,7 +6915,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
    > > target = prev_cpu;
    > >
    > > sync_entity_load_avg(&p->se);
    > > - if (!task_util_est(p))
    > > + if (!uclamp_task_util(p, p_util_min, p_util_max))
    >
    > Is it not enough to just replace the task_util_est with the
    > uclamp_task_util? If change the definition of uclamp_task_util,
    > that means it have to get task's uclamp first if user want to call the
    > function, may increase the code complex farther more?

    Calling uclamp_eff_value() all the time is not cheap actually.

    We can easily add two versions when we need to:

    __uclamp_task_util(p, uclamp_min, uclamp_max);

    uclamp_task_util(p) {
    uclamp_min = uclamp_eff_value();
    uclamp_max = uclamp_eff_value();
    return __uclamp_eff_value(p, uclamp_min, uclamp_max);
    }

    When we need to. Since we have a single user now, there's no need to do this
    now and if we ever get more users it'd be easy to refactor then?


    Thanks!

    --
    Qais Yousef

    >
    > > goto unlock;
    > >
    > > for (; pd; pd = pd->next) {
    > > --
    > > 2.25.1
    > >
    >
    > BR
    > ---
    > xuewen.yan

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