From b5fa516b3aa41f6095b4badca38273f064f434ea Mon Sep 17 00:00:00 2001
From: Quentin Perret <quentin.perret@arm.com>
Date: Tue, 30 Jul 2019 13:54:00 +0100
Subject: [PATCH] ANDROID: sched/core: Add a latency-sensitive flag to uclamp

Add a 'latency_sensitive' flag to uclamp in order to express the need
for some tasks to find a CPU where they can wake-up quickly. This is not
expected to be used without cgroup support, so add solely a cgroup
interface for it.

As this flag represents a boolean attribute and not an amount of
resources to be shared, it is not clear what the delegation logic should
be. As such, it is kept simple: every new cgroup starts with
latency_sensitive set to false, regardless of the parent.

In essence, this is similar to SchedTune's prefer-idle flag which was
used in android-4.19 and prior.

Change-Id: I722d8ecabb428bb7b95a5b54bc70a87f182dde2a
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
---
 kernel/sched/core.c  | 27 +++++++++++++++++++++++++++
 kernel/sched/sched.h |  2 ++
 2 files changed, 29 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 98d6a1b9ea8c..d99a09c485ae 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8398,6 +8398,27 @@ static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
 	cpu_uclamp_print(sf, UCLAMP_MAX);
 	return 0;
 }
+
+static int cpu_uclamp_ls_write_u64(struct cgroup_subsys_state *css,
+				   struct cftype *cftype, u64 ls)
+{
+	struct task_group *tg;
+
+	if (ls > 1)
+		return -EINVAL;
+	tg = css_tg(css);
+	tg->latency_sensitive = (unsigned int) ls;
+
+	return 0;
+}
+
+static u64 cpu_uclamp_ls_read_u64(struct cgroup_subsys_state *css,
+				  struct cftype *cft)
+{
+	struct task_group *tg = css_tg(css);
+
+	return (u64) tg->latency_sensitive;
+}
 #endif /* CONFIG_UCLAMP_TASK_GROUP */
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -8743,6 +8764,12 @@ static struct cftype cpu_files[] = {
 		.seq_show = cpu_uclamp_max_show,
 		.write = cpu_uclamp_max_write,
 	},
+	{
+		.name = "uclamp.latency_sensitive",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.read_u64 = cpu_uclamp_ls_read_u64,
+		.write_u64 = cpu_uclamp_ls_write_u64,
+	},
 #endif
 	{ }	/* Terminate */
 };
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index bdfaef874538..4dfcc887f839 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -414,6 +414,8 @@ struct task_group {
 	struct uclamp_se	uclamp_req[UCLAMP_CNT];
 	/* Effective clamp values used for a task group */
 	struct uclamp_se	uclamp[UCLAMP_CNT];
+	/* Latency-sensitive flag used for a task group */
+	unsigned int		latency_sensitive;
 #endif
 
 };