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sched/uclamp: Set max_spare_cap_cpu even if max_spare_cap is 0
When uclamp_max is being used, the util of the task could be higher than
the spare capacity of the CPU, but due to uclamp_max value we force-fit
it there.
The way the condition for checking for max_spare_cap in
find_energy_efficient_cpu() was constructed; it ignored any CPU that has
its spare_cap less than or _equal_ to max_spare_cap. Since we initialize
max_spare_cap to 0; this lead to never setting max_spare_cap_cpu and
hence ending up never performing compute_energy() for this cluster and
missing an opportunity for a better energy efficient placement to honour
uclamp_max setting.
max_spare_cap = 0;
cpu_cap = capacity_of(cpu) - cpu_util(p); // 0 if cpu_util(p) is high
...
util_fits_cpu(...); // will return true if uclamp_max forces it to fit
...
// this logic will fail to update max_spare_cap_cpu if cpu_cap is 0
if (cpu_cap > max_spare_cap) {
max_spare_cap = cpu_cap;
max_spare_cap_cpu = cpu;
}
prev_spare_cap suffers from a similar problem.
Fix the logic by converting the variables into long and treating -1
value as 'not populated' instead of 0 which is a viable and correct
spare capacity value. We need to be careful signed comparison is used
when comparing with cpu_cap in one of the conditions.
Fixes: 1d42509e47
("sched/fair: Make EAS wakeup placement consider uclamp restrictions")
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230916232955.2099394-2-qyousef@layalina.io
This commit is contained in:
parent
5fe7765997
commit
6b00a40147
1 changed files with 5 additions and 6 deletions
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@ -7703,11 +7703,10 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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for (; pd; pd = pd->next) {
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unsigned long util_min = p_util_min, util_max = p_util_max;
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unsigned long cpu_cap, cpu_thermal_cap, util;
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unsigned long cur_delta, max_spare_cap = 0;
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long prev_spare_cap = -1, max_spare_cap = -1;
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unsigned long rq_util_min, rq_util_max;
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unsigned long prev_spare_cap = 0;
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unsigned long cur_delta, base_energy;
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int max_spare_cap_cpu = -1;
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unsigned long base_energy;
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int fits, max_fits = -1;
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cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
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@ -7770,7 +7769,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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prev_spare_cap = cpu_cap;
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prev_fits = fits;
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} else if ((fits > max_fits) ||
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((fits == max_fits) && (cpu_cap > max_spare_cap))) {
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((fits == max_fits) && ((long)cpu_cap > max_spare_cap))) {
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/*
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* Find the CPU with the maximum spare capacity
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* among the remaining CPUs in the performance
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@ -7782,7 +7781,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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}
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}
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if (max_spare_cap_cpu < 0 && prev_spare_cap == 0)
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if (max_spare_cap_cpu < 0 && prev_spare_cap < 0)
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continue;
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eenv_pd_busy_time(&eenv, cpus, p);
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@ -7790,7 +7789,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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base_energy = compute_energy(&eenv, pd, cpus, p, -1);
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/* Evaluate the energy impact of using prev_cpu. */
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if (prev_spare_cap > 0) {
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if (prev_spare_cap > -1) {
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prev_delta = compute_energy(&eenv, pd, cpus, p,
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prev_cpu);
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/* CPU utilization has changed */
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