On Wed, 2012-07-11 at 22:05 +0000, Thomas Gleixner wrote:
> plain text document attachment
> (disable-rt_group_sched-in-preempt_rt_full.patch)
> Strange CPU stalls have been observed in RT when RT_GROUP_SCHED
> was configured.
>
> Disable it for now.
>
> Signed-off-by: Carsten Emde <C.Emde@xxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>
> ---
> init/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> Index: linux-3.4.4-rt13-64+/init/Kconfig
> ===================================================================
> --- linux-3.4.4-rt13-64+.orig/init/Kconfig
> +++ linux-3.4.4-rt13-64+/init/Kconfig
> @@ -746,6 +746,7 @@ config RT_GROUP_SCHED
> bool "Group scheduling for SCHED_RR/FIFO"
> depends on EXPERIMENTAL
> depends on CGROUP_SCHED
> + depends on !PREEMPT_RT_FULL
> default n
> help
> This feature lets you explicitly allocate real CPU bandwidth
>
>
>
>
>
I turn the thing off because it doesn't make any sense to me for -rt,
and because it's busted. The below works around isolation bustage I
encountered. Peter didn't like it (what's to like?) but it saves the
day, so shall live on in non-rt kernels until I hopefully someday see
RT_GROUP_SCHED being fed into a Bitwolf-9000 ;-)
sched,rt: fix isolated CPUs leaving root_task_group indefinitely throttled
Root task group bandwidth replentishment must service all CPUs regardless of
where it was last started.
Signed-off-by: Mike Galbraith <efault@xxxxxx>
---
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,
+ * 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 functionallity 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);
--
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