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Subject[patch] sched,rt: non-isolated cores lift isolcpus throttle for CONFIG_RT_GROUP_SCHED
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s/patch/hack.  Better ideas?

When CONFIG_RT_GROUP_SCHED is enabled, isolcpus have no replentishment timer
running, and unlike !CONFIG_RT_GROUP_SCHED, are not in rd->span of the cpu
running replentishment. If you trigger the throttle, you're rewarded with a
dead box. Should the user reassign cpus to a domain, they become sane again,
replentishment starts/stops as usual.

Signed-off-by: Mike Galbraith <efault@gmx.de>
---
kernel/sched/core.c | 15 ++++++++++++++-
kernel/sched/rt.c | 16 ++++++++++++++--
kernel/sched/sched.h | 5 +++++
3 files changed, 33 insertions(+), 3 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5877,6 +5877,14 @@ cpu_attach_domain(struct sched_domain *s

sched_domain_debug(sd, cpu);

+#ifdef CONFIG_RT_GROUP_SCHED
+ /* If the cpu was an isolcpu, it no longer is. */
+ if (sd) {
+ cpumask_clear_cpu(cpu, cpu_isolated_map);
+ nr_isolated_cpus = cpumask_weight(cpu_isolated_map);
+ }
+#endif
+
rq_attach_root(rq, rd);
tmp = rq->sd;
rcu_assign_pointer(rq->sd, sd);
@@ -5886,13 +5894,18 @@ cpu_attach_domain(struct sched_domain *s
}

/* cpus with isolated domains */
-static cpumask_var_t cpu_isolated_map;
+cpumask_var_t cpu_isolated_map;
+
+__read_mostly int nr_isolated_cpus;

/* Setup the mask of cpus configured for isolated domains */
static int __init isolated_cpu_setup(char *str)
{
alloc_bootmem_cpumask_var(&cpu_isolated_map);
cpulist_parse(str, cpu_isolated_map);
+#ifdef CONFIG_RT_GROUP_SCHED
+ nr_isolated_cpus = cpumask_weight(cpu_isolated_map);
+#endif
return 1;
}

--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -778,10 +778,11 @@ static inline int balance_runtime(struct

static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
{
- int i, idle = 1, throttled = 0;
+ int i, idle = 1, throttled = 0, isol_cpus = nr_isolated_cpus;
const struct cpumask *span;

span = sched_rt_period_mask();
+do_isolcpus:
for_each_cpu(i, span) {
int enqueue = 0;
struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
@@ -792,7 +793,7 @@ static int do_sched_rt_period_timer(stru
u64 runtime;

raw_spin_lock(&rt_rq->rt_runtime_lock);
- if (rt_rq->rt_throttled)
+ if (rt_rq->rt_throttled && span != cpu_isolated_map)
balance_runtime(rt_rq);
runtime = rt_rq->rt_runtime;
rt_rq->rt_time -= min(rt_rq->rt_time, overrun*runtime);
@@ -823,6 +824,17 @@ static int do_sched_rt_period_timer(stru
raw_spin_unlock(&rq->lock);
}

+ /*
+ * Hack: unthrottle isolcpus for RT_GROUP_SCHED. No replentishment
+ * timer is running on isolcpus, and unlike !RT_GROUP_SCHED, they're
+ * not in the rd->span of the cpu running the timer.
+ */
+ if (isol_cpus) {
+ span = cpu_isolated_map;
+ isol_cpus = 0;
+ goto do_isolcpus;
+ }
+
if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF))
return 1;

--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -572,6 +572,11 @@ static inline void set_task_rq(struct ta
#endif
}

+/* cpus with isolated domains */
+extern cpumask_var_t cpu_isolated_map;
+
+extern __read_mostly int nr_isolated_cpus;
+
#else /* CONFIG_CGROUP_SCHED */

static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }



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