Commit ab278921 authored Dec 15, 2011 by Peter Zijlstra Committed by Ingo Molnar Dec 16, 2011

sched: Fix select_idle_sibling() regression in selecting an idle SMT sibling



Mike Galbraith reported that this recent commit:

   commit 4dcfe102
   Author: Peter Zijlstra <peterz@infradead.org>
   Date:   Thu Nov 10 13:01:10 2011 +0100

       sched: Avoid SMT siblings in select_idle_sibling() if possible

stopped selecting an idle SMT sibling when there are no idle
cores in a single socket system.

Intent of the select_idle_sibling() was to fallback to an idle
SMT sibling, if it fails to identify an idle core. But this
fallback was not happening on systems where all the scheduler
domains had `SD_SHARE_PKG_RESOURCES' flag set.

Fix it. Slightly bigger patch of cleaning all these goto's etc
is queued up for the next release.

Reported-by: Mike Galbraith <efault@gmx.de>
Reported-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1323978421.1984.244.camel@sbsiddha-desk.sc.intel.com


Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 75fc2d37

kernel/sched_fair.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -2352,13 +2352,11 @@ again:
		if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
		continue;

		if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
		if (!smt) {
		smt = 1;
		goto again;
		}
		if (smt && !(sd->flags & SD_SHARE_CPUPOWER))
		break;

		if (!(sd->flags & SD_SHARE_PKG_RESOURCES))
		break;
		}

		sg = sd->groups;
		do {
		@@ -2378,6 +2376,10 @@ next:
		sg = sg->next;
		} while (sg != sd->groups);
		}
		if (!smt) {
		smt = 1;
		goto again;
		}
		done:
		rcu_read_unlock();

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