[tip: sched/core] sched/fair: unlink misfit task from cpu overutilized

From: tip-bot2 for Vincent Guittot
Date: Sat Feb 11 2023 - 05:31:12 EST

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The following commit has been merged into the sched/core branch of tip:

Commit-ID: e5ed0550c04c5469ecdc1634d8aa18c8609590f0
Gitweb: https://git.kernel.org/tip/e5ed0550c04c5469ecdc1634d8aa18c8609590f0
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
AuthorDate: Wed, 01 Feb 2023 15:36:27 +01:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Sat, 11 Feb 2023 11:18:09 +01:00

sched/fair: unlink misfit task from cpu overutilized

By taking into account uclamp_min, the 1:1 relation between task misfit
and cpu overutilized is no more true as a task with a small util_avg may
not fit a high capacity cpu because of uclamp_min constraint.

Add a new state in util_fits_cpu() to reflect the case that task would fit
a CPU except for the uclamp_min hint which is a performance requirement.

Use -1 to reflect that a CPU doesn't fit only because of uclamp_min so we
can use this new value to take additional action to select the best CPU
that doesn't match uclamp_min hint.

When util_fits_cpu() returns -1, we will continue to look for a possible
CPU with better performance, which replaces Capacity Inversion detection
with capacity_orig_of() - thermal_load_avg to detect a capacity inversion.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Reviewed-and-tested-by: Qais Yousef <qyousef@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Tested-by: Kajetan Puchalski <kajetan.puchalski@xxxxxxx>
Link: https://lore.kernel.org/r/20230201143628.270912-2-vincent.guittot@xxxxxxxxxx
---
kernel/sched/fair.c | 105 +++++++++++++++++++++++++++++++++----------
1 file changed, 82 insertions(+), 23 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7c46485..074742f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4561,8 +4561,8 @@ static inline int util_fits_cpu(unsigned long util,
* handle the case uclamp_min > uclamp_max.
*/
uclamp_min = min(uclamp_min, uclamp_max);
- if (util < uclamp_min && capacity_orig != SCHED_CAPACITY_SCALE)
- fits = fits && (uclamp_min <= capacity_orig_thermal);
+ if (fits && (util < uclamp_min) && (uclamp_min > capacity_orig_thermal))
+ return -1;

return fits;
}
@@ -4572,7 +4572,11 @@ static inline int task_fits_cpu(struct task_struct *p, int cpu)
unsigned long uclamp_min = uclamp_eff_value(p, UCLAMP_MIN);
unsigned long uclamp_max = uclamp_eff_value(p, UCLAMP_MAX);
unsigned long util = task_util_est(p);
- return util_fits_cpu(util, uclamp_min, uclamp_max, cpu);
+ /*
+ * Return true only if the cpu fully fits the task requirements, which
+ * include the utilization but also the performance hints.
+ */
+ return (util_fits_cpu(util, uclamp_min, uclamp_max, cpu) > 0);
}

static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
@@ -6138,6 +6142,7 @@ static inline bool cpu_overutilized(int cpu)
unsigned long rq_util_min = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MIN);
unsigned long rq_util_max = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MAX);

+ /* Return true only if the utilization doesn't fit CPU's capacity */
return !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu);
}

@@ -6931,6 +6936,7 @@ static int
select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
{
unsigned long task_util, util_min, util_max, best_cap = 0;
+ int fits, best_fits = 0;
int cpu, best_cpu = -1;
struct cpumask *cpus;

@@ -6946,12 +6952,28 @@ select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)

if (!available_idle_cpu(cpu) && !sched_idle_cpu(cpu))
continue;
- if (util_fits_cpu(task_util, util_min, util_max, cpu))
+
+ fits = util_fits_cpu(task_util, util_min, util_max, cpu);
+
+ /* This CPU fits with all requirements */
+ if (fits > 0)
return cpu;
+ /*
+ * Only the min performance hint (i.e. uclamp_min) doesn't fit.
+ * Look for the CPU with best capacity.
+ */
+ else if (fits < 0)
+ cpu_cap = capacity_orig_of(cpu) - thermal_load_avg(cpu_rq(cpu));

- if (cpu_cap > best_cap) {
+ /*
+ * First, select CPU which fits better (-1 being better than 0).
+ * Then, select the one with best capacity at same level.
+ */
+ if ((fits < best_fits) ||
+ ((fits == best_fits) && (cpu_cap > best_cap))) {
best_cap = cpu_cap;
best_cpu = cpu;
+ best_fits = fits;
}
}

@@ -6964,7 +6986,11 @@ static inline bool asym_fits_cpu(unsigned long util,
int cpu)
{
if (sched_asym_cpucap_active())
- return util_fits_cpu(util, util_min, util_max, cpu);
+ /*
+ * Return true only if the cpu fully fits the task requirements
+ * which include the utilization and the performance hints.
+ */
+ return (util_fits_cpu(util, util_min, util_max, cpu) > 0);

return true;
}
@@ -7331,6 +7357,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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;
+ int prev_fits = -1, best_fits = -1;
+ unsigned long best_thermal_cap = 0;
+ unsigned long prev_thermal_cap = 0;
struct sched_domain *sd;
struct perf_domain *pd;
struct energy_env eenv;
@@ -7366,6 +7395,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
unsigned long prev_spare_cap = 0;
int max_spare_cap_cpu = -1;
unsigned long base_energy;
+ int fits, max_fits = -1;

cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);

@@ -7415,7 +7445,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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))
+
+ fits = util_fits_cpu(util, util_min, util_max, cpu);
+ if (!fits)
continue;

lsub_positive(&cpu_cap, util);
@@ -7423,7 +7455,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
if (cpu == prev_cpu) {
/* Always use prev_cpu as a candidate. */
prev_spare_cap = cpu_cap;
- } else if (cpu_cap > max_spare_cap) {
+ prev_fits = fits;
+ } else if ((fits > max_fits) ||
+ ((fits == max_fits) && (cpu_cap > max_spare_cap))) {
/*
* Find the CPU with the maximum spare capacity
* among the remaining CPUs in the performance
@@ -7431,6 +7465,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
*/
max_spare_cap = cpu_cap;
max_spare_cap_cpu = cpu;
+ max_fits = fits;
}
}

@@ -7449,26 +7484,50 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
if (prev_delta < base_energy)
goto unlock;
prev_delta -= base_energy;
+ prev_thermal_cap = cpu_thermal_cap;
best_delta = min(best_delta, prev_delta);
}

/* Evaluate the energy impact of using max_spare_cap_cpu. */
if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) {
+ /* Current best energy cpu fits better */
+ if (max_fits < best_fits)
+ continue;
+
+ /*
+ * Both don't fit performance hint (i.e. uclamp_min)
+ * but best energy cpu has better capacity.
+ */
+ if ((max_fits < 0) &&
+ (cpu_thermal_cap <= best_thermal_cap))
+ continue;
+
cur_delta = compute_energy(&eenv, pd, cpus, p,
max_spare_cap_cpu);
/* CPU utilization has changed */
if (cur_delta < base_energy)
goto unlock;
cur_delta -= base_energy;
- if (cur_delta < best_delta) {
- best_delta = cur_delta;
- best_energy_cpu = max_spare_cap_cpu;
- }
+
+ /*
+ * Both fit for the task but best energy cpu has lower
+ * energy impact.
+ */
+ if ((max_fits > 0) && (best_fits > 0) &&
+ (cur_delta >= best_delta))
+ continue;
+
+ best_delta = cur_delta;
+ best_energy_cpu = max_spare_cap_cpu;
+ best_fits = max_fits;
+ best_thermal_cap = cpu_thermal_cap;
}
}
rcu_read_unlock();

- if (best_delta < prev_delta)
+ if ((best_fits > prev_fits) ||
+ ((best_fits > 0) && (best_delta < prev_delta)) ||
+ ((best_fits < 0) && (best_thermal_cap > prev_thermal_cap)))
target = best_energy_cpu;

return target;
@@ -10271,24 +10330,23 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
*/
update_sd_lb_stats(env, &sds);

- if (sched_energy_enabled()) {
- struct root_domain *rd = env->dst_rq->rd;
-
- if (rcu_dereference(rd->pd) && !READ_ONCE(rd->overutilized))
- goto out_balanced;
- }
-
- local = &sds.local_stat;
- busiest = &sds.busiest_stat;
-
/* There is no busy sibling group to pull tasks from */
if (!sds.busiest)
goto out_balanced;

+ busiest = &sds.busiest_stat;
+
/* Misfit tasks should be dealt with regardless of the avg load */
if (busiest->group_type == group_misfit_task)
goto force_balance;

+ if (sched_energy_enabled()) {
+ struct root_domain *rd = env->dst_rq->rd;
+
+ if (rcu_dereference(rd->pd) && !READ_ONCE(rd->overutilized))
+ goto out_balanced;
+ }
+
/* ASYM feature bypasses nice load balance check */
if (busiest->group_type == group_asym_packing)
goto force_balance;
@@ -10301,6 +10359,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
if (busiest->group_type == group_imbalanced)
goto force_balance;

+ local = &sds.local_stat;
/*
* If the local group is busier than the selected busiest group
* don't try and pull any tasks.

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