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Commit 3a5a6747 authored by Pavankumar Kondeti's avatar Pavankumar Kondeti Committed by Gerrit - the friendly Code Review server
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sched/fair: Add fallback CPU selection 



When all CPUs are overloaded, the task is placed on the previous
CPU during wakeup. This can result in packing high number of tasks
on a CPU. When no suitable CPU is found and previous CPU has more
than 32 runnable tasks, add a fallback CPU selection to find
the CPU with least number of runnable tasks.

When a CPU is isolated or hotplugged out, all tasks queued on
the CPU are migrated to CPU#0. This can result in packing high
number of tasks on CPU#0. Add the above fallback CPU selection
here also.

Change-Id: Ia9b959339692770b4cc594fa36cf42ca342cf2de
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent 3de6f27e

kernel/sched/core.c

+13 −2
Original line number Diff line number Diff line
@@ -2092,6 +2092,8 @@ static int select_fallback_rq(int cpu, struct task_struct *p, bool allow_iso) 
	enum { cpuset, possible, fail, bug } state = cpuset;

	int dest_cpu;

	int isolated_candidate = -1;

	int backup_cpu = -1;

	unsigned int max_nr = UINT_MAX;



	/*

	 * If the node that the CPU is on has been offlined, cpu_to_node()
@@ -2107,9 +2109,18 @@ static int select_fallback_rq(int cpu, struct task_struct *p, bool allow_iso) 
				continue;

			if (cpu_isolated(dest_cpu))

				continue;

			if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed))

			if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed)) {

				if (cpu_rq(dest_cpu)->nr_running < 32)

					return dest_cpu;

				if (cpu_rq(dest_cpu)->nr_running > max_nr)

					continue;

				backup_cpu = dest_cpu;

				max_nr = cpu_rq(dest_cpu)->nr_running;

			}

		}



		if (backup_cpu != -1)

			return backup_cpu;

	}



	for (;;) {

kernel/sched/fair.c

+20 −1
Original line number Diff line number Diff line
@@ -7765,8 +7765,27 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu, 


	/* Bail out if no candidate was found. */

	weight = cpumask_weight(candidates);

	if (!weight)

	if (!weight) {

		/*

		 * Don't overload the previous CPU if it had already

		 * more runnable tasks. Fallback to a CPU with lower

		 * number of tasks.

		 */

		if (cpu_rq(prev_cpu)->nr_running > 32) {

			int i;

			unsigned int best_nr = UINT_MAX;



			for_each_cpu(i, cpu_active_mask) {

				if (!cpumask_test_cpu(i, &p->cpus_allowed))

					continue;

				if (cpu_rq(i)->nr_running < best_nr) {

					best_nr = cpu_rq(i)->nr_running;

					best_energy_cpu = i;

				}

			}

		}

		goto unlock;

	}



	/* If there is only one sensible candidate, select it now. */

	cpu = cpumask_first(candidates);