[PATCH 6.0 0096/1073] sched/uclamp: Fix fits_capacity() check in feec()

Greg Kroah-Hartman
2022-12-28T15:05:46Z

From: Qais Yousef <qais.yousef@arm.com>

[ Upstream commit 244226035a1f9b2b6c326e55ae5188fab4f428cb ]

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220804143609.515789-4-qais.yousef@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/sched/core.c | 10 +++++-----
kernel/sched/fair.c | 26 ++++++++++++++++++++++++--
kernel/sched/sched.h | 42 +++++++++++++++++++++++++++++++++++++++---
3 files changed, 68 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee28253c9ac0..cb9d8ae7c4db 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1398,7 +1398,7 @@ 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
@@ -1549,8 +1549,8 @@ 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);
}

/*
@@ -1616,7 +1616,7 @@ 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.
@@ -1624,7 +1624,7 @@ 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 fd0eb93e1bbb..abe0e6baaa2e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6993,6 +6993,8 @@ 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;
@@ -7025,6 +7027,8 @@ 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;
@@ -7061,8 +7065,26 @@ 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);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1b8a5d791907..0dfcd12e184a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2963,6 +2963,23 @@ 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.
@@ -2998,12 +3015,12 @@ 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
@@ -3066,6 +3083,25 @@ 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
--
2.35.1