linux-kernel - [PATCH 02/17] sched/fair: Add latency

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Message-ID: <20230328110353.711028613@infradead.org>
Date:   Tue, 28 Mar 2023 11:26:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, vincent.guittot@...aro.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, corbet@....net, qyousef@...alina.io,
        chris.hyser@...cle.com, patrick.bellasi@...bug.net, pjt@...gle.com,
        pavel@....cz, qperret@...gle.com, tim.c.chen@...ux.intel.com,
        joshdon@...gle.com, timj@....org, kprateek.nayak@....com,
        yu.c.chen@...el.com, youssefesmat@...omium.org,
        joel@...lfernandes.org, efault@....de
Subject: [PATCH 02/17] sched/fair: Add latency_offset

From: Vincent Guittot <vincent.guittot@...aro.org>


Murdered-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@....com>
---
 include/linux/sched.h |    2 ++
 kernel/sched/core.c   |   12 +++++++++++-
 kernel/sched/fair.c   |    8 ++++++++
 kernel/sched/sched.h  |    2 ++
 4 files changed, 23 insertions(+), 1 deletion(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -568,6 +568,8 @@ struct sched_entity {
 	/* cached value of my_q->h_nr_running */
 	unsigned long			runnable_weight;
 #endif
+	/* preemption offset in ns */
+	long				latency_offset;
 
 #ifdef CONFIG_SMP
 	/*
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1285,6 +1285,11 @@ static void set_load_weight(struct task_
 	}
 }
 
+static void set_latency_offset(struct task_struct *p)
+{
+	p->se.latency_offset = calc_latency_offset(p->latency_prio - MAX_RT_PRIO);
+}
+
 #ifdef CONFIG_UCLAMP_TASK
 /*
  * Serializes updates of utilization clamp values
@@ -4433,6 +4438,8 @@ static void __sched_fork(unsigned long c
 	p->se.vruntime			= 0;
 	INIT_LIST_HEAD(&p->se.group_node);
 
+	set_latency_offset(p);
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	p->se.cfs_rq			= NULL;
 #endif
@@ -4685,6 +4692,7 @@ int sched_fork(unsigned long clone_flags
 		set_load_weight(p, false);
 
 		p->latency_prio = NICE_TO_PRIO(0);
+		set_latency_offset(p);
 
 		/*
 		 * We don't need the reset flag anymore after the fork. It has
@@ -7457,8 +7465,10 @@ static void __setscheduler_params(struct
 static void __setscheduler_latency(struct task_struct *p,
 				   const struct sched_attr *attr)
 {
-	if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE)
+	if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE) {
 		p->latency_prio = NICE_TO_PRIO(attr->sched_latency_nice);
+		set_latency_offset(p);
+	}
 }
 
 /*
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -703,6 +703,14 @@ int sched_update_scaling(void)
 }
 #endif
 
+long calc_latency_offset(int prio)
+{
+	u32 weight = sched_prio_to_weight[prio];
+	u64 base = sysctl_sched_min_granularity;
+
+	return div_u64(base << SCHED_FIXEDPOINT_SHIFT, weight);
+}
+
 /*
  * delta /= w
  */
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2475,6 +2475,8 @@ extern unsigned int sysctl_numa_balancin
 extern unsigned int sysctl_numa_balancing_hot_threshold;
 #endif
 
+extern long calc_latency_offset(int prio);
+
 #ifdef CONFIG_SCHED_HRTICK
 
 /*