[PATCH] sched/uclamp: Introduce a method to transform UCLAMP_MIN into BOOST

[Xuewen Yan]

From: Xuewen Yan <xuewen.yan@xxxxxxxxxx>

The uclamp can clamp the util within uclamp_min and uclamp_max,
it is benifit to some tasks with small util, but for those tasks
with middle util, it is useless.

To speed up those tasks, convert UCLAMP_MIN to BOOST,
the BOOST as schedtune does:

boot = uclamp_min / SCHED_CAPACITY_SCALE;
margin = boost * (uclamp_max - util)
boost_util = util + margin;

Scenario:
if the task_util = 200, {uclamp_min, uclamp_max} = {100, 1024}

without patch:
clamp_util = 200;

with patch:
clamp_util = 200 + (100 / 1024) * (1024 - 200) = 280;

On the other hand, adding a SYS interface to  allow users
to configure it according to their own needs.

Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
---
 include/linux/sched/sysctl.h |  1 +
 kernel/sched/core.c          | 19 +++++++++++++++++++
 kernel/sched/fair.c          | 15 ++++++++++++---
 kernel/sched/sched.h         | 10 +++++++++-
 kernel/sysctl.c              |  9 +++++++++
 5 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index db2c0f34aaaf..97d8c5ecd4e6 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -69,6 +69,7 @@ extern unsigned int sysctl_sched_dl_period_min;
 extern unsigned int sysctl_sched_uclamp_util_min;
 extern unsigned int sysctl_sched_uclamp_util_max;
 extern unsigned int sysctl_sched_uclamp_util_min_rt_default;
+extern unsigned int sysctl_sched_uclamp_min_to_boost;
 #endif
 
 #ifdef CONFIG_CFS_BANDWIDTH
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2d9ff40f4661..8a49f9962cda 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1245,6 +1245,9 @@ unsigned int sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;
  */
 unsigned int sysctl_sched_uclamp_util_min_rt_default = SCHED_CAPACITY_SCALE;
 
+/* map util clamp_min to boost */
+unsigned int sysctl_sched_uclamp_min_to_boost;
+
 /* All clamps are required to be less or equal than these values */
 static struct uclamp_se uclamp_default[UCLAMP_CNT];
 
@@ -1448,6 +1451,22 @@ uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
 	return uc_req;
 }
 
+unsigned long uclamp_transform_boost(unsigned long util, unsigned long uclamp_min,
+				    unsigned long uclamp_max)
+{
+	unsigned long margin;
+
+	if (unlikely(uclamp_min > uclamp_max))
+		return util;
+
+	if (util >= uclamp_max)
+		return uclamp_max;
+
+	margin = DIV_ROUND_CLOSEST_ULL(uclamp_min * (uclamp_max - util),
+					SCHED_CAPACITY_SCALE);
+	return util + margin;
+}
+
 unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
 {
 	struct uclamp_se uc_eff;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 44c452072a1b..790dfbb6c897 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3934,9 +3934,18 @@ static inline unsigned long task_util_est(struct task_struct *p)
 #ifdef CONFIG_UCLAMP_TASK
 static inline unsigned long uclamp_task_util(struct task_struct *p)
 {
-	return clamp(task_util_est(p),
-		     uclamp_eff_value(p, UCLAMP_MIN),
-		     uclamp_eff_value(p, UCLAMP_MAX));
+	unsigned long min_util = uclamp_eff_value(p, UCLAMP_MIN);
+	unsigned long max_util = uclamp_eff_value(p, UCLAMP_MAX);
+	unsigned long clamp_util, util;
+
+	util = task_util_est(p);
+
+	if (sysctl_sched_uclamp_min_to_boost)
+		clamp_util = uclamp_transform_boost(util, min_util, max_util);
+	else
+		clamp_util = clamp(util, min_util, max_util);
+
+	return clamp_util;
 }
 #else
 static inline unsigned long uclamp_task_util(struct task_struct *p)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 14a41a243f7b..73657be84678 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2796,6 +2796,8 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
 
 #ifdef CONFIG_UCLAMP_TASK
 unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);
+unsigned long uclamp_transform_boost(unsigned long util, unsigned long uclamp_min,
+				     unsigned long uclamp_max);
 
 /**
  * uclamp_rq_util_with - clamp @util with @rq and @p effective uclamp values.
@@ -2820,6 +2822,7 @@ unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
 {
 	unsigned long min_util = 0;
 	unsigned long max_util = 0;
+	unsigned long clamp_util;
 
 	if (!static_branch_likely(&sched_uclamp_used))
 		return util;
@@ -2847,7 +2850,12 @@ unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
 	if (unlikely(min_util >= max_util))
 		return min_util;
 
-	return clamp(util, min_util, max_util);
+	if (sysctl_sched_uclamp_min_to_boost)
+		clamp_util = uclamp_transform_boost(util, min_util, max_util);
+	else
+		clamp_util = clamp(util, min_util, max_util);
+
+	return clamp_util;
 }
 
 /*
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 272f4a272f8c..b3a83356a969 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1827,6 +1827,15 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= sysctl_sched_uclamp_handler,
 	},
+	{
+		.procname	= "sched_clamp_min2boost",
+		.data		= &sysctl_sched_uclamp_min_to_boost,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
 #endif
 #ifdef CONFIG_SCHED_AUTOGROUP
 	{
-- 
2.25.1