HMP: experimental: Force all rt tasks to start on little domain.

This patch restricts the allowed cpu mask for rt tasks initially started
with a full cpu mask to the little domain.

An rt task is specified as real time in __setscheduler() which is finally
called for all rt tasks (kernel and user land). In this function we
restrict the allowed cpu mask to the little domain.

This also prevents that a rt tasks can later be pushed to the big domain
because the function find_lowest_rq() will only recognize the allowed cpu
mask of a task to find the new cpu the task runs on.

Current kludges of the patch:

* Since we do not have an API to get the cpu mask of the A7 cluster,
hmp_slow_cpu_mask is made global in arm/kernel/topology.c for now.

* The watchdog_enable() function calls sched_setscheduler() before
kthread_bind() for the cpu specific watchdog kernel threads. The order of
these two calls has to be changed to make this patch work.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 9047dd1c5a1..4459c0b4e91 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -367,10 +367,11 @@ void __init arch_get_fast_and_slow_cpus(struct cpumask *fast,
 	cpumask_clear(slow);
 }
 
+struct cpumask hmp_slow_cpu_mask;
+
 void __init arch_get_hmp_domains(struct list_head *hmp_domains_list)
 {
 	struct cpumask hmp_fast_cpu_mask;
-	struct cpumask hmp_slow_cpu_mask;
 	struct hmp_domain *domain;
 
 	arch_get_fast_and_slow_cpus(&hmp_fast_cpu_mask, &hmp_slow_cpu_mask);