This is a note to let you know that I've just added the patch titled
sched/rt: Fix SCHED_RR across cgroups
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-rt-fix-sched_rr-across-cgroups.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 454c79999f7eaedcdf4c15c449e43902980cbdf5 Mon Sep 17 00:00:00 2001
From: Colin Cross <ccross@xxxxxxxxxxx>
Date: Wed, 16 May 2012 21:34:23 -0700
Subject: sched/rt: Fix SCHED_RR across cgroups
From: Colin Cross <ccross@xxxxxxxxxxx>
commit 454c79999f7eaedcdf4c15c449e43902980cbdf5 upstream.
task_tick_rt() has an optimization to only reschedule SCHED_RR tasks
if they were the only element on their rq. However, with cgroups
a SCHED_RR task could be the only element on its per-cgroup rq but
still be competing with other SCHED_RR tasks in its parent's
cgroup. In this case, the SCHED_RR task in the child cgroup would
never yield at the end of its timeslice. If the child cgroup
rt_runtime_us was the same as the parent cgroup rt_runtime_us,
the task in the parent cgroup would starve completely.
Modify task_tick_rt() to check that the task is the only task on its
rq, and that the each of the scheduling entities of its ancestors
is also the only entity on its rq.
Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1337229266-15798-1-git-send-email-ccross@xxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/rt.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1997,6 +1997,8 @@ static void watchdog(struct rq *rq, stru
static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
{
+ struct sched_rt_entity *rt_se = &p->rt;
+
update_curr_rt(rq);
watchdog(rq, p);
@@ -2014,12 +2016,15 @@ static void task_tick_rt(struct rq *rq,
p->rt.time_slice = RR_TIMESLICE;
/*
- * Requeue to the end of queue if we are not the only element
- * on the queue:
+ * Requeue to the end of queue if we (and all of our ancestors) are the
+ * only element on the queue
*/
- if (p->rt.run_list.prev != p->rt.run_list.next) {
- requeue_task_rt(rq, p, 0);
- set_tsk_need_resched(p);
+ for_each_sched_rt_entity(rt_se) {
+ if (rt_se->run_list.prev != rt_se->run_list.next) {
+ requeue_task_rt(rq, p, 0);
+ set_tsk_need_resched(p);
+ return;
+ }
}
}
Patches currently in stable-queue which might be from ccross@xxxxxxxxxxx are
queue-3.4/sched-rt-fix-sched_rr-across-cgroups.patch
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