Messages in this thread Patch in this message | | | Date | Fri, 5 Sep 2008 18:00:04 +0530 | From | Gautham R Shenoy <> | Subject | [PATCH] sched: Fix __load_balance_iterator() for cfq with only one task |
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sched: Fix __load_balance_iterator() for cfq with only one task.
From: Gautham R Shenoy <ego@in.ibm.com>
The __load_balance_iterator() returns a NULL when there's only one sched_entity which is a task. It is caused by the following code-path.
/* Skip over entities that are not tasks */ do { se = list_entry(next, struct sched_entity, group_node); next = next->next; } while (next != &cfs_rq->tasks && !entity_is_task(se));
if (next == &cfs_rq->tasks) return NULL; ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This will return NULL even when se is a task.
As a side-effect, there was a regression in sched_mc behavior since 2.6.25, since iter_move_one_task() when it calls load_balance_start_fair(), would not get any tasks to move!
Fix this by checking if the last entity was a task or not.
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> ---
kernel/sched_fair.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index fb8994c..f1c96e3 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1451,7 +1451,7 @@ __load_balance_iterator(struct cfs_rq *cfs_rq, struct list_head *next) next = next->next; } while (next != &cfs_rq->tasks && !entity_is_task(se)); - if (next == &cfs_rq->tasks) + if (next == &cfs_rq->tasks && !entity_is_task(se)) return NULL; cfs_rq->balance_iterator = next; -- Thanks and Regards gautham
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