Messages in this thread Patch in this message | | | From | Pierre Gondois <> | Subject | [PATCH 1/2] sched/fair: Check if prev_cpu has highest spare cap in feec() | Date | Fri, 19 Aug 2022 17:33:19 +0200 |
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When evaluating the CPU candidates in the perf domain (pd) containing the previously used CPU (prev_cpu), find_energy_efficient_cpu() evaluates the energy of the pd: - without the task (base_energy) - with the task placed on prev_cpu (if the task fits) - with the task placed on the CPU with the highest spare capacity, prev_cpu being excluded from this set
If prev_cpu is already the CPU with the highest spare capacity, max_spare_cap_cpu will be the CPU with the second highest spare capacity.
On an Arm64 Juno-r2, with a workload of 10 tasks at a 10% duty cycle, when prev_cpu and max_spare_cap_cpu are both valid candidates, prev_spare_cap > max_spare_cap at ~82%. Thus the energy of the pd when placing the task on max_spare_cap_cpu is computed with no possible positive outcome 82% most of the time.
Do not consider max_spare_cap_cpu as a valid candidate if prev_spare_cap > max_spare_cap.
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com> --- kernel/sched/fair.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 914096c5b1ae..bcae7bdd5582 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6900,7 +6900,7 @@ 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; - bool compute_prev_delta = false; + unsigned long prev_spare_cap = 0; int max_spare_cap_cpu = -1; unsigned long base_energy; @@ -6944,18 +6944,19 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) if (cpu == prev_cpu) { /* Always use prev_cpu as a candidate. */ - compute_prev_delta = true; + prev_spare_cap = cpu_cap; } else if (cpu_cap > max_spare_cap) { /* * Find the CPU with the maximum spare capacity - * in the performance domain. + * among the remaining CPUs in the performance + * domain. */ max_spare_cap = cpu_cap; max_spare_cap_cpu = cpu; } } - if (max_spare_cap_cpu < 0 && !compute_prev_delta) + if (max_spare_cap_cpu < 0 && prev_spare_cap == 0) continue; eenv_pd_busy_time(&eenv, cpus, p); @@ -6963,7 +6964,7 @@ 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 (compute_prev_delta) { + if (prev_spare_cap > 0) { prev_delta = compute_energy(&eenv, pd, cpus, p, prev_cpu); /* CPU utilization has changed */ @@ -6974,7 +6975,7 @@ 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) { + if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) { cur_delta = compute_energy(&eenv, pd, cpus, p, max_spare_cap_cpu); /* CPU utilization has changed */ -- 2.25.1
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