Commit e790fb0b authored Apr 14, 2009 by Gautham R Shenoy Committed by Ingo Molnar Apr 14, 2009

sched: Nominate a power-efficient ilb in select_nohz_balancer()



The CPU that first goes idle becomes the idle-load-balancer and remains
that until either it picks up a task or till all the CPUs of the system
goes idle.

Optimize this further to allow it to relinquish it's post
once all it's siblings in the power-aware sched_domain go idle, thereby
allowing the whole package-core to go idle. While relinquising the post,
nominate another an idle-load balancer from a semi-idle core/package.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090414045535.7645.31641.stgit@sofia.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent f711f609

kernel/sched.c

+17 −1

Original line number	Diff line number	Diff line
		@@ -4414,8 +4414,24 @@ int select_nohz_load_balancer(int stop_tick)
		/* make me the ilb owner */
		if (atomic_cmpxchg(&nohz.load_balancer, -1, cpu) == -1)
		return 1;
		} else if (atomic_read(&nohz.load_balancer) == cpu)
		} else if (atomic_read(&nohz.load_balancer) == cpu) {
		int new_ilb;

		if (!(sched_smt_power_savings \|\|
		sched_mc_power_savings))
		return 1;
		/*
		* Check to see if there is a more power-efficient
		* ilb.
		*/
		new_ilb = find_new_ilb(cpu);
		if (new_ilb < nr_cpu_ids && new_ilb != cpu) {
		atomic_set(&nohz.load_balancer, -1);
		resched_cpu(new_ilb);
		return 0;
		}
		return 1;
		}
		} else {
		if (!cpumask_test_cpu(cpu, nohz.cpu_mask))
		return 0;