On 12/05/15 20:39, Morten Rasmussen wrote:
> Let available compute capacity and estimated energy impact select
> wake-up target cpu when energy-aware scheduling is enabled and the
> system in not over-utilized (above the tipping point).
>
> energy_aware_wake_cpu() attempts to find group of cpus with sufficient
> compute capacity to accommodate the task and find a cpu with enough spare
> capacity to handle the task within that group. Preference is given to
> cpus with enough spare capacity at the current OPP. Finally, the energy
> impact of the new target and the previous task cpu is compared to select
> the wake-up target cpu.
>
> cc: Ingo Molnar <mi...@redhat.com>
> cc: Peter Zijlstra <pet...@infradead.org>
>
> Signed-off-by: Morten Rasmussen <morten.rasmus...@arm.com>
[...]
> /*
> * select_task_rq_fair: Select target runqueue for the waking task in domains
> * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
> @@ -5446,7 +5526,10 @@ select_task_rq_fair(struct task_struct *p, int
> prev_cpu, int sd_flag, int wake_f
> prev_cpu = cpu;
>
> if (sd_flag & SD_BALANCE_WAKE && want_sibling) {
> - new_cpu = select_idle_sibling(p, prev_cpu);
> + if (energy_aware() && !cpu_rq(cpu)->rd->overutilized)
> + new_cpu = energy_aware_wake_cpu(p);
If you run RFCv4 on an X86 system w/o energy model, you get a
'BUG: unable to handle kernel paging request at ...' problem after you've
enabled
energy awareness (echo ENERGY_AWARE > /sys/kernel/debug/sched_features).
This is related to the fact that cpumask functions like cpumask_test_cpu
(e.g. later in select_task_rq) can't deal with cpu set to -1.
If you enable CONFIG_DEBUG_PER_CPU_MAPS you get the following warning in this
case:
WARNING: CPU: 0 PID: 0 at include/linux/cpumask.h:117
cpumask_check.part.79+0x1f/0x30()
We also get the warning on ARM (w/o energy model) but my TC2 system is not
crashing
like the X86 box.
Shouldn't we return prev_cpu in case sd_ea is NULL just as select_idle_sibling
does
if prev_cpu is idle?
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f5897a021f23..8a014fdd6e76 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5394,7 +5394,7 @@ static int select_idle_sibling(struct task_struct *p, int
target)
return target;
}
-static int energy_aware_wake_cpu(struct task_struct *p)
+static int energy_aware_wake_cpu(struct task_struct *p, int target)
{
struct sched_domain *sd;
struct sched_group *sg, *sg_target;
@@ -5405,7 +5405,7 @@ static int energy_aware_wake_cpu(struct task_struct *p)
sd = rcu_dereference(per_cpu(sd_ea, task_cpu(p)));
if (!sd)
- return -1;
+ return target;
sg = sd->groups;
sg_target = sg;
@@ -5527,7 +5527,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu,
int sd_flag, int wake_f
if (sd_flag & SD_BALANCE_WAKE && want_sibling) {
if (energy_aware() && !cpu_rq(cpu)->rd->overutilized)
- new_cpu = energy_aware_wake_cpu(p);
+ new_cpu = energy_aware_wake_cpu(p, prev_cpu);
else
new_cpu = select_idle_sibling(p, prev_cpu);
goto unlock;
> + else
> + new_cpu = select_idle_sibling(p, prev_cpu);
> goto unlock;
> }
--
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