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

Mike Galbraith reported that this recent commit:

   commit 4dcfe1025b
   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>
This commit is contained in:
Peter Zijlstra 2011-12-15 11:47:00 -08:00 committed by Ingo Molnar
parent 75fc2d3797
commit ab2789213d
1 changed files with 8 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
kernel/sched_fair.c
View File

@ -2352,13 +2352,11 @@ static int select_idle_sibling(struct task_struct *p, int target)
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 @@ static int select_idle_sibling(struct task_struct *p, int target)
sg = sg->next;
} while (sg != sd->groups);
}
if (!smt) {
smt = 1;
goto again;
}
done:
rcu_read_unlock();