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sched/uclamp: Fix fits_capacity() check in feec()

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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: 1d42509e47 ("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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220804143609.515789-4-qais.yousef@arm.com
This commit is contained in:
Qais Yousef 2022-08-04 15:36:03 +01:00 committed by Peter Zijlstra
parent b48e16a697
commit 244226035a
3 changed files with 68 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
kernel/sched/core.c
View File

@ -1392,7 +1392,7 @@ 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
@ -1543,8 +1543,8 @@ 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);
}
/*
@ -1610,7 +1610,7 @@ 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.
@ -1618,7 +1618,7 @@ 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);
}
}

26
kernel/sched/fair.c
View File

@ -7169,6 +7169,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
{
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
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 = this_rq()->rd;
int cpu, best_energy_cpu, target = -1;
struct sched_domain *sd;
@ -7201,6 +7203,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
for (; pd; pd = pd->next) {
unsigned long cpu_cap, cpu_thermal_cap, util;
unsigned long cur_delta, max_spare_cap = 0;
unsigned long rq_util_min, rq_util_max;
unsigned long util_min, util_max;
bool compute_prev_delta = false;
int max_spare_cap_cpu = -1;
unsigned long base_energy;
@ -7237,8 +7241,26 @@ 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;
lsub_positive(&cpu_cap, util);

42
kernel/sched/sched.h
View File

@ -2979,6 +2979,23 @@ 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;
}
/**
* uclamp_rq_util_with - clamp @util with @rq and @p effective uclamp values.
* @rq: The rq to clamp against. Must not be NULL.
@ -3014,12 +3031,12 @@ unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
* Ignore last runnable task's max clamp, as this task will
* reset it. Similarly, no need to read the rq's min clamp.
*/
if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
if (uclamp_rq_is_idle(rq))
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
@ -3082,6 +3099,25 @@ 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