Messages in this thread Patch in this message |  | | From | Qais Yousef <> | Subject | [PATCH 1/3] sched/uclamp: Set max_spare_cap_cpu even if max_spare_cap is 0 | Date | Sun, 29 Jan 2023 16:14:42 +0000 |
| |
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) - task_util(p); // 0 if task_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 treating -1UL value as 'not populated' instead of 0 which is a viable and correct spare capacity value.
Fixes: 1d42509e475c ("sched/fair: Make EAS wakeup placement consider uclamp restrictions") Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> --- kernel/sched/fair.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e29e9ea4cde8..ca2c389d3180 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7390,9 +7390,9 @@ 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; + unsigned long cur_delta, max_spare_cap = -1UL; unsigned long rq_util_min, rq_util_max; - unsigned long prev_spare_cap = 0; + unsigned long prev_spare_cap = -1UL; int max_spare_cap_cpu = -1; unsigned long base_energy; int fits, max_fits = -1; @@ -7457,7 +7457,8 @@ 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) && + (cpu_cap > max_spare_cap || max_spare_cap == -1UL) { /* * Find the CPU with the maximum spare capacity * among the remaining CPUs in the performance @@ -7469,7 +7470,7 @@ 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 == -1UL) continue; eenv_pd_busy_time(&eenv, cpus, p); @@ -7477,7 +7478,7 @@ 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 != -1UL) { prev_delta = compute_energy(&eenv, pd, cpus, p, prev_cpu); /* CPU utilization has changed */ @@ -7489,7 +7490,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) } /* Evaluate the energy impact of using max_spare_cap_cpu. */ - if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) { + if (max_spare_cap_cpu >= 0 && + (max_spare_cap > prev_spare_cap || prev_spare_cap == -1UL)) { /* Current best energy cpu fits better */ if (max_fits < best_fits) continue; -- 2.25.1
|  |