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SubjectRe: RFC [patch] sched,cgroup_sched: convince RT_GROUP_SCHED throttle to work
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On Tue, 2012-04-10 at 11:08 +0200, Mike Galbraith wrote:

> sched,rt: fix isolated CPUs leaving root_task_group indefinitely throttled
>
> Root task group bandwidth replenishment must service all CPUs regardless of
> where it was last started.
>
> Signed-off-by: Mike Galbraith <efault@gmx.de>
> ---
> kernel/sched/rt.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -782,6 +782,19 @@ static int do_sched_rt_period_timer(stru
> const struct cpumask *span;
>
> span = sched_rt_period_mask();
> +#ifdef CONFIG_RT_GROUP_SCHED
> + /*
> + * FIXME: isolated CPUs should really leave the root task group,

No no, that's the wrong fix, the right fix is to remove isolcpus :-)

> + * 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;
> +#endif
> for_each_cpu(i, span) {
> int enqueue = 0;
> struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);

I guess the alternative 'fix' is to not account the rt_runtime on
isolated cpus.. does something like the below actually work?

---
kernel/sched/rt.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 44af55e..dc2b5b6 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -922,6 +922,9 @@ static void update_curr_rt(struct rq *rq)
if (!rt_bandwidth_enabled())
return;

+ if (cpumask_test_cpu(cpu_of(rq), cpu_isolated_map))
+ return;
+
for_each_sched_rt_entity(rt_se) {
rt_rq = rt_rq_of_se(rt_se);



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