diff options
| author | Qais Yousef <qyousef@layalina.io> | 2023-09-17 00:29:53 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2023-09-29 10:29:14 +0200 |
| commit | 6b00a40147653c8ea748e8f4396510f252763364 (patch) | |
| tree | 4d7d49864400518e168e47196730beb0fb4c109f /kernel/sched | |
| parent | 5fe7765997b139e2d922b58359dea181efe618f9 (diff) | |
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: 1d42509e475c ("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
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/fair.c | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2973173ad850..4ce949bb0213 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7703,11 +7703,10 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) for (; pd; pd = pd->next) { unsigned long util_min = p_util_min, util_max = p_util_max; unsigned long cpu_cap, cpu_thermal_cap, util; - unsigned long cur_delta, max_spare_cap = 0; + long prev_spare_cap = -1, max_spare_cap = -1; unsigned long rq_util_min, rq_util_max; - unsigned long prev_spare_cap = 0; + unsigned long cur_delta, base_energy; 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); @@ -7770,7 +7769,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) prev_spare_cap = cpu_cap; prev_fits = fits; } else if ((fits > max_fits) || - ((fits == max_fits) && (cpu_cap > max_spare_cap))) { + ((fits == max_fits) && ((long)cpu_cap > max_spare_cap))) { /* * Find the CPU with the maximum spare capacity * among the remaining CPUs in the performance @@ -7782,7 +7781,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) } } - if (max_spare_cap_cpu < 0 && prev_spare_cap == 0) + if (max_spare_cap_cpu < 0 && prev_spare_cap < 0) continue; eenv_pd_busy_time(&eenv, cpus, p); @@ -7790,7 +7789,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) base_energy = compute_energy(&eenv, pd, cpus, p, -1); /* Evaluate the energy impact of using prev_cpu. */ - if (prev_spare_cap > 0) { + if (prev_spare_cap > -1) { prev_delta = compute_energy(&eenv, pd, cpus, p, prev_cpu); /* CPU utilization has changed */ |