Commit f29c9b1c authored Nov 06, 2008 by Li Zefan Committed by Ingo Molnar Nov 07, 2008

sched: fix a bug in sched domain degenerate



Impact: re-add incorrectly eliminated sched domain layers

(1) on i386 with SCHED_SMT and SCHED_MC enabled
	# mount -t cgroup -o cpuset xxx /mnt
	# echo 0 > /mnt/cpuset.sched_load_balance
	# mkdir /mnt/0
	# echo 0 > /mnt/0/cpuset.cpus
	# dmesg
	CPU0 attaching sched-domain:
	 domain 0: span 0 level CPU
	  groups: 0

(2) on i386 with SCHED_MC enabled but SCHED_SMT disabled
	# same with (1)
	# dmesg
	CPU0 attaching NULL sched-domain.

The bug is that some sched domains may be skipped unintentionally when
degenerating (optimizing) sched domains.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 4bab0ea1

kernel/sched.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -6877,15 +6877,17 @@ cpu_attach_domain(struct sched_domain sd, struct root_domain rd, int cpu)
		struct sched_domain *tmp;

		/* Remove the sched domains which do not contribute to scheduling. */
		for (tmp = sd; tmp; tmp = tmp->parent) {
		for (tmp = sd; tmp; ) {
		struct sched_domain *parent = tmp->parent;
		if (!parent)
		break;

		if (sd_parent_degenerate(tmp, parent)) {
		tmp->parent = parent->parent;
		if (parent->parent)
		parent->parent->child = tmp;
		}
		} else
		tmp = tmp->parent;
		}

		if (sd && sd_degenerate(sd)) {

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