kernel: Restore schedtune compatibility

When SCHED_TUNE is disabled, certain elements in userspace, like
libperfmgr, may throw errors when it doesn't detect SCHEDTUNE-related nodes.
So, create a few dummy nodes to satisfy said userspace elements.

Change-Id: I24df608349551c94d4b50d0764548bd669e5a770
Signed-off-by: darkhz <[email protected]>
Signed-off-by: Panchajanya1999 <[email protected]>

include/linux/cgroup_subsys.h

@@ -21,7 +21,7 @@ SUBSYS(cpu)
 SUBSYS(cpuacct)
 #endif
 
-#if IS_ENABLED(CONFIG_SCHED_TUNE)
+#if IS_ENABLED(CONFIG_SCHED_TUNE) || IS_ENABLED(CONFIG_SCHED_TUNE_DUMMY)
 SUBSYS(schedtune)
 #endif
 

init/Kconfig

@@ -1106,6 +1106,13 @@ config SCHED_TUNE
 
 	  If unsure, say N.
 
+config SCHED_TUNE_DUMMY
+	bool "Create dummy SCHEDTUNE nodes"
+	depends on SMP
+	depends on !SCHED_TUNE
+	help
+	  Create dummy SCHEDTUNE nodes.
+
 config DEFAULT_USE_ENERGY_AWARE
 	bool "Default to enabling the Energy Aware Scheduler feature"
 	default n

kernel/sched/Makefile

@@ -26,6 +26,7 @@ obj-$(CONFIG_SCHED_AUTOGROUP) += autogroup.o
 obj-$(CONFIG_SCHEDSTATS) += stats.o
 obj-$(CONFIG_SCHED_DEBUG) += debug.o
 obj-$(CONFIG_SCHED_TUNE) += tune.o
+obj-$(CONFIG_SCHED_TUNE_DUMMY) += tune_dummy.o
 obj-$(CONFIG_CGROUP_CPUACCT) += cpuacct.o
 obj-$(CONFIG_CPU_FREQ) += cpufreq.o
 obj-$(CONFIG_CPU_FREQ_GOV_SCHEDUTIL) += cpufreq_schedutil.o

kernel/sched/tune_dummy.c

@@ -0,0 +1,122 @@
+#include <linux/cgroup.h>
+#include "sched.h"
+
+#define BOOSTGROUPS_COUNT 5
+
+struct schedtune {
+	/* SchedTune CGroup subsystem */
+	struct cgroup_subsys_state css;
+
+	/* Boost value for tasks on that SchedTune CGroup */
+	int boost;
+
+	/* Hint to bias scheduling of tasks on that SchedTune CGroup
+	 * towards idle CPUs */
+	int prefer_idle;
+};
+
+static struct schedtune
+root_schedtune = {
+	.boost	= 0,
+	.prefer_idle = 0,
+};
+
+static struct schedtune *allocated_group[BOOSTGROUPS_COUNT] = {
+	&root_schedtune,
+	NULL,
+};
+
+static inline struct schedtune *css_st(struct cgroup_subsys_state *css)
+{
+	return container_of(css, struct schedtune, css);
+}
+
+static u64
+prefer_idle_read(struct cgroup_subsys_state *css, struct cftype *cft)
+{
+	return 0;
+}
+
+static int
+prefer_idle_write(struct cgroup_subsys_state *css, struct cftype *cft,
+	    u64 prefer_idle)
+{
+	return 0;
+}
+
+static s64
+boost_read(struct cgroup_subsys_state *css, struct cftype *cft)
+{
+	return 0;
+}
+
+static int
+boost_write(struct cgroup_subsys_state *css, struct cftype *cft,
+	    s64 boost)
+{
+	return 0;
+}
+
+static struct cftype files[] = {
+	{
+		.name = "boost",
+		.read_s64 = boost_read,
+		.write_s64 = boost_write,
+	},
+	{
+		.name = "prefer_idle",
+		.read_u64 = prefer_idle_read,
+		.write_u64 = prefer_idle_write,
+	},
+	{ }	/* terminate */
+};
+
+static struct cgroup_subsys_state *
+schedtune_css_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct schedtune *st;
+	int idx;
+
+	if (!parent_css)
+		return &root_schedtune.css;
+
+	/* Allow only single level hierachies */
+	if (parent_css != &root_schedtune.css) {
+		pr_err("Nested SchedTune boosting groups not allowed\n");
+		return ERR_PTR(-ENOMEM);
+	}
+
+	/* Allow only a limited number of boosting groups */
+	for (idx = 1; idx < BOOSTGROUPS_COUNT; ++idx)
+		if (!allocated_group[idx])
+			break;
+	if (idx == BOOSTGROUPS_COUNT) {
+		pr_err("Trying to create more than %d SchedTune boosting groups\n",
+		       BOOSTGROUPS_COUNT);
+		return ERR_PTR(-ENOSPC);
+	}
+
+	st = kzalloc(sizeof(*st), GFP_KERNEL);
+	if (!st)
+		goto out;
+
+	return &st->css;
+
+out:
+	return ERR_PTR(-ENOMEM);
+}
+
+static void
+schedtune_css_free(struct cgroup_subsys_state *css)
+{
+	struct schedtune *st = css_st(css);
+
+	kfree(st);
+}
+
+struct cgroup_subsys schedtune_cgrp_subsys = {
+	.css_alloc	= schedtune_css_alloc,
+	.css_free	= schedtune_css_free,
+	.legacy_cftypes	= files,
+	.early_init	= 1,
+};