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>

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 9047dd1c5a12f1cdd33a10dde31c8a1acf41b5a2..4459c0b4e915939546c8b834c83212b338e696b2 100644 (file)
--- 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);

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4c53da3781e08f67258328268cea97ee8f15e79b..50d9e9849ce75ae89ae9fb46fa7a1f4674035477 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3827,6 +3827,8 @@ static struct task_struct *find_process_by_pid(pid_t pid)
        return pid ? find_task_by_vpid(pid) : current;
 }
 
+extern struct cpumask hmp_slow_cpu_mask;
+
 /* Actually do priority change: must hold rq lock. */
 static void
 __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
@@ -3836,8 +3838,13 @@ __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
        p->normal_prio = normal_prio(p);
        /* we are holding p->pi_lock already */
        p->prio = rt_mutex_getprio(p);
-       if (rt_prio(p->prio))
+       if (rt_prio(p->prio)) {
                p->sched_class = &rt_sched_class;
+#ifdef CONFIG_SCHED_HMP
+               if (cpumask_equal(&p->cpus_allowed, cpu_all_mask))
+                       do_set_cpus_allowed(p, &hmp_slow_cpu_mask);
+#endif
+       }
        else
                p->sched_class = &fair_sched_class;
        set_load_weight(p);