Commit 83f462da authored Mar 08, 2017 by Chris Redpath Committed by Andres Oportus Jun 02, 2017

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>

parent 8865f076

kernel/sched/fair.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -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);