From: Leo Yan leo.yan@linaro.org
The homescreen test-case shows unwanted disturbance on the big CPUs on the Hikey620 platform with Android 4.9. There are multiple reasons for that though.
By default boost and prefer_idle are enabled for both top-app and foreground tasks and find_best_target() always (intentionally) prefers the big CPUs if prefer_idle is enabled. And some of the foreground tasks (like: DispSync, PowerManagerSer and PhotonicModulat) for the homescreen test-case get placed on the big CPUs eventually because of that.
Even if prefer_idle is disabled for such foreground tasks, they don't end up on the little CPUs. The reason being that find_best_target() still prefers big CPUs if the task is boosted, though some of the comments in find_best_target() routine say the exact opposite of that. It eventually depends on the order in which CPUs are processed, which is from big to little for boosted tasks.
This patch updates the find_best_target() routine to select low capacity idle-CPU if the task is boosted but doesn't have prefer_idle enabled. This would be the same for non-boosted tasks as well.
Signed-off-by: Leo Yan leo.yan@linaro.org Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- kernel/sched/fair.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e45047bdd245..4534d8620989 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6998,8 +6998,11 @@ static inline int find_best_target(struct task_struct *p, int *backup_cpu, int idle_idx = idle_get_state_idx(cpu_rq(i));
/* Select idle CPU with lower cap_orig */ - if (capacity_orig > best_idle_min_cap_orig) + if (capacity_orig < best_idle_min_cap_orig) + goto found_best_idle_cpu; + else if (capacity_orig > best_idle_min_cap_orig) continue; + /* Favor CPUs that won't end up running at a * high OPP. */ @@ -7017,6 +7020,7 @@ static inline int find_best_target(struct task_struct *p, int *backup_cpu, best_idle_cstate <= idle_idx) continue;
+found_best_idle_cpu: /* Keep track of best idle CPU */ best_idle_min_cap_orig = capacity_orig; target_idle_max_spare_cap = capacity_orig - -- 2.15.0.194.g9af6a3dea062