sched/fair: ensure utilization signals are synchronized before use

wake_cap performs task and cpu utilization synchronization which is
what allows us to subtract current task util from prev_cpu util and
have a sensible number to work with.

It looks as though if wake_wide returns 0, we could potentially not
execute wake_cap, which would result in unsynced signals we then use
for energy calculations.

This is not necessarily an issue we've seen in traces, but it looks
as though it should be changed.

Change-Id: Ic54a3cba2a10d946ea20113a04371dea04115e82
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 27a6f5d6c86c6a7d0b5bdab6b08ee5b22fc1da63..23e2b5f33ff6df40b9551d4fe43b0eefe1396244 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6424,9 +6424,16 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
        int want_affine = 0;
        int sync = wake_flags & WF_SYNC;
 
-       if (sd_flag & SD_BALANCE_WAKE)
-               want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)
+       if (sd_flag & SD_BALANCE_WAKE) {
+               /*
+                * do wake_cap unconditionally as it causes task and cpu
+                * utilization to be synced, and we need that for energy
+                * aware wakeups
+                */
+               int _wake_cap = wake_cap(p, cpu, prev_cpu);
+               want_affine = !wake_wide(p) && !_wake_cap
                              && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
+       }
 
        if (energy_aware() && !(cpu_rq(prev_cpu)->rd->overutilized))
                return select_energy_cpu_brute(p, prev_cpu, sync);