[RFC][PATCH 12/16] sched: A quick and dirty cgroup tagging interface

[Peter Zijlstra]

Marks all tasks in a cgroup as matching for core-scheduling.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/core.c  |   62 +++++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/sched/sched.h |    4 +++
 2 files changed, 66 insertions(+)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6608,6 +6608,15 @@ static void sched_change_group(struct ta
 	tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
 			  struct task_group, css);
 	tg = autogroup_task_group(tsk, tg);
+
+#ifdef CONFIG_SCHED_CORE
+	if ((unsigned long)tsk->sched_task_group == tsk->core_cookie)
+		tsk->core_cookie = 0UL;
+
+	if (tg->tagged /* && !tsk->core_cookie ? */)
+		tsk->core_cookie = (unsigned long)tg;
+#endif
+
 	tsk->sched_task_group = tg;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -7067,6 +7076,43 @@ static u64 cpu_rt_period_read_uint(struc
 }
 #endif /* CONFIG_RT_GROUP_SCHED */
 
+#ifdef CONFIG_SCHED_CORE
+static u64 cpu_core_tag_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
+{
+	struct task_group *tg = css_tg(css);
+
+	return !!tg->tagged;
+}
+
+static int cpu_core_tag_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, u64 val)
+{
+	struct task_group *tg = css_tg(css);
+	struct css_task_iter it;
+	struct task_struct *p;
+
+	if (val > 1)
+		return -ERANGE;
+
+	if (tg->tagged == !!val)
+		return 0;
+
+	tg->tagged = !!val;
+
+	if (!!val)
+		sched_core_get();
+
+	css_task_iter_start(css, 0, &it);
+	while ((p = css_task_iter_next(&it)))
+		p->core_cookie = !!val ? (unsigned long)tg : 0UL;
+	css_task_iter_end(&it);
+
+	if (!val)
+		sched_core_put();
+
+	return 0;
+}
+#endif
+
 static struct cftype cpu_legacy_files[] = {
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	{
@@ -7103,6 +7149,14 @@ static struct cftype cpu_legacy_files[]
 		.write_u64 = cpu_rt_period_write_uint,
 	},
 #endif
+#ifdef CONFIG_SCHED_CORE
+	{
+		.name = "tag",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.read_u64 = cpu_core_tag_read_u64,
+		.write_u64 = cpu_core_tag_write_u64,
+	},
+#endif
 	{ }	/* Terminate */
 };
 
@@ -7270,6 +7324,14 @@ static struct cftype cpu_files[] = {
 		.write = cpu_max_write,
 	},
 #endif
+#ifdef CONFIG_SCHED_CORE
+	{
+		.name = "tag",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.read_u64 = cpu_core_tag_read_u64,
+		.write_u64 = cpu_core_tag_write_u64,
+	},
+#endif
 	{ }	/* terminate */
 };
 
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -363,6 +363,10 @@ struct cfs_bandwidth {
 struct task_group {
 	struct cgroup_subsys_state css;
 
+#ifdef CONFIG_SCHED_CORE
+	int			tagged;
+#endif
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	/* schedulable entities of this group on each CPU */
 	struct sched_entity	**se;