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    SubjectRe: [PATCH 3/7] sched/uclamp: Fix fits_capacity() check in feec()
    Hi Qais

    On Thu, Jun 30, 2022 at 3:48 AM Qais Yousef <qais.yousef@arm.com> wrote:
    >
    > As reported by Yun Hsiang [1], if a task has its uclamp_min >= 0.8 * 1024,
    > it'll always pick the previous CPU because fits_capacity() will always
    > return false in this case.
    >
    > The new util_fits_cpu() logic should handle this correctly for us beside
    > more corner cases where similar failures could occur, like when using
    > UCLAMP_MAX.
    >
    > We open code uclamp_rq_util_with() except for the clamp() part,
    > util_fits_cpu() needs the 'raw' values to be passed to it.
    >
    > Also introduce uclamp_rq_{set, get}() shorthand accessors to get uclamp
    > value for the rq. Makes the code more readable and ensures the right
    > rules (use READ_ONCE/WRITE_ONCE) are respected transparently.
    >
    > [1] https://lists.linaro.org/pipermail/eas-dev/2020-July/001488.html
    >
    > Fixes: 1d42509e475c ("sched/fair: Make EAS wakeup placement consider uclamp restrictions")
    > Reported-by: Yun Hsiang <hsiang023167@gmail.com>
    > Signed-off-by: Qais Yousef <qais.yousef@arm.com>
    > ---
    > kernel/sched/core.c | 10 +++++-----
    > kernel/sched/fair.c | 26 ++++++++++++++++++++++++--
    > kernel/sched/sched.h | 40 ++++++++++++++++++++++++++++++++++++++--
    > 3 files changed, 67 insertions(+), 9 deletions(-)
    >
    > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    > index d3e2c5a7c1b7..f5dac570d6c5 100644
    > --- a/kernel/sched/core.c
    > +++ b/kernel/sched/core.c
    > @@ -1404,7 +1404,7 @@ static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
    > if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
    > return;
    >
    > - WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
    > + uclamp_rq_set(rq, clamp_id, clamp_value);
    > }
    >
    > static inline
    > @@ -1555,8 +1555,8 @@ static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
    > if (bucket->tasks == 1 || uc_se->value > bucket->value)
    > bucket->value = uc_se->value;
    >
    > - if (uc_se->value > READ_ONCE(uc_rq->value))
    > - WRITE_ONCE(uc_rq->value, uc_se->value);
    > + if (uc_se->value > uclamp_rq_get(rq, clamp_id))
    > + uclamp_rq_set(rq, clamp_id, uc_se->value);
    > }
    >
    > /*
    > @@ -1622,7 +1622,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
    > if (likely(bucket->tasks))
    > return;
    >
    > - rq_clamp = READ_ONCE(uc_rq->value);
    > + rq_clamp = uclamp_rq_get(rq, clamp_id);
    > /*
    > * Defensive programming: this should never happen. If it happens,
    > * e.g. due to future modification, warn and fixup the expected value.
    > @@ -1630,7 +1630,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
    > SCHED_WARN_ON(bucket->value > rq_clamp);
    > if (bucket->value >= rq_clamp) {
    > bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
    > - WRITE_ONCE(uc_rq->value, bkt_clamp);
    > + uclamp_rq_set(rq, clamp_id, bkt_clamp);
    > }
    > }
    >
    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index 313437bea5a2..c80c676ab1bc 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -6878,6 +6878,8 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
    > static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
    > {
    > unsigned long prev_delta = ULONG_MAX, best_delta = ULONG_MAX;
    > + unsigned long p_util_min = uclamp_is_used() ? uclamp_eff_value(p, UCLAMP_MIN) : 0;
    > + unsigned long p_util_max = uclamp_is_used() ? uclamp_eff_value(p, UCLAMP_MAX) : 1024;
    > struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
    > int cpu, best_energy_cpu = prev_cpu, target = -1;
    > unsigned long cpu_cap, util, base_energy = 0;
    > @@ -6907,6 +6909,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
    >
    > for (; pd; pd = pd->next) {
    > unsigned long cur_delta, spare_cap, max_spare_cap = 0;
    > + unsigned long rq_util_min, rq_util_max;
    > + unsigned long util_min, util_max;
    > bool compute_prev_delta = false;
    > unsigned long base_energy_pd;
    > int max_spare_cap_cpu = -1;
    > @@ -6927,8 +6931,26 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
    > * much capacity we can get out of the CPU; this is
    > * aligned with sched_cpu_util().
    > */
    > - util = uclamp_rq_util_with(cpu_rq(cpu), util, p);
    > - if (!fits_capacity(util, cpu_cap))
    > + if (uclamp_is_used()) {
    > + if (uclamp_rq_is_idle(cpu_rq(cpu))) {
    > + util_min = p_util_min;
    > + util_max = p_util_max;
    > + } else {
    > + /*
    > + * Open code uclamp_rq_util_with() except for
    > + * the clamp() part. Ie: apply max aggregation
    > + * only. util_fits_cpu() logic requires to
    > + * operate on non clamped util but must use the
    > + * max-aggregated uclamp_{min, max}.
    > + */
    > + rq_util_min = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MIN);
    > + rq_util_max = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MAX);
    > +
    > + util_min = max(rq_util_min, p_util_min);
    > + util_max = max(rq_util_max, p_util_max);
    > + }
    > + }
    > + if (!util_fits_cpu(util, util_min, util_max, cpu))
    > continue;
    >
    > if (cpu == prev_cpu) {
    > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    > index 9599d2eea3e7..69c4d35988b9 100644
    > --- a/kernel/sched/sched.h
    > +++ b/kernel/sched/sched.h
    > @@ -2907,6 +2907,23 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
    > #ifdef CONFIG_UCLAMP_TASK
    > unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);
    >
    > +static inline unsigned long uclamp_rq_get(struct rq *rq,
    > + enum uclamp_id clamp_id)
    > +{
    > + return READ_ONCE(rq->uclamp[clamp_id].value);
    > +}
    > +
    > +static inline void uclamp_rq_set(struct rq *rq, enum uclamp_id clamp_id,
    > + unsigned int value)
    > +{
    > + WRITE_ONCE(rq->uclamp[clamp_id].value, value);
    > +}
    > +
    > +static inline bool uclamp_rq_is_idle(struct rq *rq)
    > +{
    > + return rq->uclamp_flags & UCLAMP_FLAG_IDLE;
    > +}

    Can you replace the idle judgment in the uclamp_rq_util_with()
    function by the way?

    > +
    > /**
    > * uclamp_rq_util_with - clamp @util with @rq and @p effective uclamp values.
    > * @rq: The rq to clamp against. Must not be NULL.
    > @@ -2946,8 +2963,8 @@ unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
    > goto out;
    > }
    >
    > - min_util = max_t(unsigned long, min_util, READ_ONCE(rq->uclamp[UCLAMP_MIN].value));
    > - max_util = max_t(unsigned long, max_util, READ_ONCE(rq->uclamp[UCLAMP_MAX].value));
    > + min_util = max_t(unsigned long, min_util, uclamp_rq_get(rq, UCLAMP_MIN));
    > + max_util = max_t(unsigned long, max_util, uclamp_rq_get(rq, UCLAMP_MAX));
    > out:
    > /*
    > * Since CPU's {min,max}_util clamps are MAX aggregated considering
    > @@ -3010,6 +3027,25 @@ static inline bool uclamp_is_used(void)
    > {
    > return false;
    > }
    > +
    > +static inline unsigned long uclamp_rq_get(struct rq *rq,
    > + enum uclamp_id clamp_id)
    > +{
    > + if (clamp_id == UCLAMP_MIN)
    > + return 0;
    > +
    > + return SCHED_CAPACITY_SCALE;
    > +}
    > +
    > +static inline void uclamp_rq_set(struct rq *rq, enum uclamp_id clamp_id,
    > + unsigned int value)
    > +{
    > +}
    > +
    > +static inline bool uclamp_rq_is_idle(struct rq *rq)
    > +{
    > + return false;
    > +}
    > #endif /* CONFIG_UCLAMP_TASK */
    >
    > #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
    > --
    > 2.25.1
    >

    Thanks!
    BR
    ----
    xuewen.yan

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