diff options
| author | Pierre Gondois <pierre.gondois@arm.com> | 2022-10-06 10:10:52 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-10-27 11:01:20 +0200 |
| commit | ad841e569f5c88e3332b32a000f251f33ff32187 (patch) | |
| tree | 3639305c4da4227530170297590eee542eb1adf9 /kernel/sched | |
| parent | aa69c36f31aadc1669bfa8a3de6a47b5e6c98ee8 (diff) | |
| download | linux-stable-ad841e569f5c88e3332b32a000f251f33ff32187.tar.gz linux-stable-ad841e569f5c88e3332b32a000f251f33ff32187.tar.bz2 linux-stable-ad841e569f5c88e3332b32a000f251f33ff32187.zip | |
sched/fair: Check if prev_cpu has highest spare cap in feec()
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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20221006081052.3862167-2-pierre.gondois@arm.com
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/fair.c | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 919d016c5d77..4cc56c91e06e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7221,7 +7221,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) unsigned long cur_delta, max_spare_cap = 0; unsigned long rq_util_min, rq_util_max; unsigned long util_min, util_max; - bool compute_prev_delta = false; + unsigned long prev_spare_cap = 0; int max_spare_cap_cpu = -1; unsigned long base_energy; @@ -7283,18 +7283,19 @@ 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); @@ -7302,7 +7303,7 @@ 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 */ @@ -7313,7 +7314,7 @@ 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 */ |