Commit 84589336 authored Sep 30, 2016 by Syed Rameez Mustafa

sched: Fix CPU selection when all online CPUs are isolated

After the introduction of "33c24b sched: add cpu isolation support"
select_fallback_rq() might sometimes be unable find any CPU to place
a task on. This happens when the all online CPUs are isolated and
the allow isolated flag is set to false. In such cases, we have
little choice but to use an isolated CPU and wait for core control
to eventually un-isolate one or more online CPUs.

Change-Id: Id8738bd8493c11731c5491efcc99eb90f051233e
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>

parent 46692be6

kernel/sched/core.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -1590,7 +1590,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p, bool allow_iso)
		{
		int nid = cpu_to_node(cpu);
		const struct cpumask *nodemask = NULL;
		enum { cpuset, possible, fail } state = cpuset;
		enum { cpuset, possible, fail, bug } state = cpuset;
		int dest_cpu;
		int isolated_candidate = -1;

		@@ -1650,6 +1650,11 @@ static int select_fallback_rq(int cpu, struct task_struct *p, bool allow_iso)
		break;

		case fail:
		allow_iso = true;
		state = bug;
		break;

		case bug:
		BUG();
		break;
		}