From: Hailong Liu <liu.hailo...@zte.com.cn>
The rq->rd->span of a cpu in a system with isolated cpus splited into two
different parts: one is for isolated cpus, another for non-isolated cpus.
When CONFIG_RT_GROUP_SCHED enabled, the handler of sched_rt_period_timer
updates rt_time and rt_runtime for every cpus in rq(this_cpu)->rd->span.
It means that other parts cpus out of this_cpu's rd->span will be missed
by sched_rt_period_timer handler, when CONFIG_RT_GROUP_SCHED enabled and
isolated cpus presents in system.
E.g problem will be triggered as follows on my 8 cores machine:
1 enable CONFIG_RT_GROUP_SCHED=y, and boot kernel with command-line
"isolcpus=4-7"
2 create a child group and init it:
mount -t cgroup -o cpu cpu /sys/fs/cgruop
mkdir /sys/fs/cgroup/child0
echo 950000 > /sys/fs/cgroup/child0/cpu.rt_runtime_us
3 run two rt-loop tasks, assume their pids are $pid1 and $pid2
4 affinity a rt task to the isolated cpu-sets
taskset -p 0xf0 $pid2
5 add tasks created above into child cpu-group
echo $pid1 > /sys/fs/cgroup/child0/tasks
echo $pid2 > /sys/fs/cgroup/child0/tasks
6 check wat happened:
"top": one of the task will fail to has cpu usage, but its stat is "R"
"kill": the task on the problem rt_rq can't be killed
This patch will fix this problem.
Signed-off-by: Hailong Liu <liu.hailo...@zte.com.cn>
---
kernel/sched/rt.c | 15 +++------------
1 file changed, 3 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 49ec096a8..c5c39695c 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -855,19 +855,10 @@ static int do_sched_rt_period_timer(struct rt_bandwidth
*rt_b, int overrun)
int i, idle = 1, throttled = 0;
const struct cpumask *span;
- span = sched_rt_period_mask();
#ifdef CONFIG_RT_GROUP_SCHED
- /*
- * FIXME: isolated CPUs should really leave the root task group,
- * whether they are isolcpus or were isolated via cpusets, lest
- * the timer run on a CPU which does not service all runqueues,
- * potentially leaving other CPUs indefinitely throttled. If
- * isolation is really required, the user will turn the throttle
- * off to kill the perturbations it causes anyway. Meanwhile,
- * this maintains functionality for boot and/or troubleshooting.
- */
- if (rt_b == &root_task_group.rt_bandwidth)
- span = cpu_online_mask;
+ span = cpu_online_mask;
+#else
+ span = sched_rt_period_mask();
#endif
for_each_cpu(i, span) {
int enqueue = 0;
--
2.17.1
