ANDROID: cpu/hotplug: rebuild sched domains immediately

In the resume_cpus() path, cpus cannot be taken
advantage of until the cpus write lock is acquired,
and cpus are activated and domains rebuilt.  This
can incurr significant delay in the unpause operation.

Additionally, if scheduled through the kworker thread,
the wait time for rebuilding sched domains becomes
large due to a busy system that can prevent the kworker
from executing.

Activate the cpus and call the cpuset_hotplug_workfn
directly within resume_cpus prior to getting the cpus
write lock, thereby eliminating delays associated
with scheduling this activity.

Bug: 161210528
Change-Id: Ie2521f28ed9078b22d421d792f08413016d4dd62
Signed-off-by: Stephen Dickey <dickey@codeaurora.org>
Signed-off-by: Todd Kjos <tkjos@google.com>

kernel/cpu.c

@@ -33,6 +33,7 @@
 #include <linux/slab.h>
 #include <linux/percpu-rwsem.h>
 #include <uapi/linux/sched/types.h>
+#include <linux/cpuset.h>
 
 #include <trace/events/power.h>
 #define CREATE_TRACE_POINTS
@@ -1253,6 +1254,15 @@ int resume_cpus(struct cpumask *cpus)
 	if (cpumask_empty(cpus))
 		goto err_cpu_maps_update;
 
+	for_each_cpu(cpu, cpus)
+		set_cpu_active(cpu, true);
+
+	/* Lazy Resume.  Build domains immediately instead of scheduling
+	 * a workqueue.  This is so that the cpu can pull load when
+	 * sent a load balancing kick.
+	 */
+	cpuset_hotplug_workfn(NULL);
+
 	cpus_write_lock();
 
 	cpuhp_tasks_frozen = 0;