[PATCH v5 1/2] sched/deadline: Add cpudl_maximum_dl() for better readability

[PATCH v5 1/2] sched/deadline: Add cpudl_maximum_dl() for better readability

[Byungchul Park]

Changes from v4
 - Fix a typo in cpudl_init() of the 2nd patch

Changes from v3
 - Rebase onto the latest tip/sched/core
 - Apply what Joel suggests, to set cp->elements[0].cpu to -1
   when the heap becomes empty in cpudl_clear()

Changes from v2
 - Run spellchecker over the text and fix typos
 - Add acked-by Daniel

Changes from v1
 - Enhance commit msg
 - Prevent WARN in cpumask_test_cpu() in cpudl_find() when best_cpu == -1

-----8<-----
>From 13efb279e8189e454062854fb1ce2df407543630 Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Mon, 4 Jun 2018 15:12:50 +0900
Subject: [PATCH v5 1/2] sched/deadline: Add cpudl_maximum_dl() for better
 readability

Current code uses cpudl_maximum() to get the root node's cpu, while it
directly accesses the root node to get the root node's dl. It would be
more readable and consistent between them if we provide the same way to
access them. So add a function for dl as we did it for cpu.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Daniel Bristot de Oliveira <bristot@redhat.com>
---
 kernel/sched/cpudeadline.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 5031645..ae4fbdc 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -105,11 +105,16 @@ static void cpudl_heapify(struct cpudl *cp, int idx)
 		cpudl_heapify_down(cp, idx);
 }
 
-static inline int cpudl_maximum(struct cpudl *cp)
+static inline int cpudl_maximum_cpu(struct cpudl *cp)
 {
 	return cp->elements[0].cpu;
 }
 
+static inline u64 cpudl_maximum_dl(struct cpudl *cp)
+{
+	return cp->elements[0].dl;
+}
+
 /*
  * cpudl_find - find the best (later-dl) CPU in the system
  * @cp: the cpudl max-heap context
@@ -127,12 +132,12 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
 	    cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
 		return 1;
 	} else {
-		int best_cpu = cpudl_maximum(cp);
+		int best_cpu = cpudl_maximum_cpu(cp);
 
 		WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
 
 		if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) &&
-		    dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
+		    dl_time_before(dl_se->deadline, cpudl_maximum_dl(cp))) {
 			if (later_mask)
 				cpumask_set_cpu(best_cpu, later_mask);
 
-- 
1.9.1

[PATCH v5 2/2] sched/deadline: Set cp->elements[0].cpu to -1 when the heap is empty

[Byungchul Park]

Hello Steven and Daniel,

I've changed the 2nd patch a little bit to consider cpudl_clear()
additionally. Can I keep your Acked-by on?

(I temporarily removed the Acked-by you gave me.)

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Daniel Bristot de Oliveira <bristot@redhat.com>

-----8<-----
>From 1e368d276186c22f9da298206c718b33e805828d Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Mon, 4 Jun 2018 15:05:08 +0900
Subject: [PATCH v5 2/2] sched/deadline: Set cp->elements[0].cpu to -1 when the
 heap is empty

Currently, migrating tasks to cpu0 unconditionally happens when the
heap is empty, since cp->elements[0].cpu is initialized to 0(=cpu0).
We have to distinguish between the empty case and cpu0 to avoid the
unnecessary migrations. Therefore, it has to return an invalid value
e.i. -1 in the case the heap is empty.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Suggested-by: Joel Fernandes <joelaf@google.com>
---
 kernel/sched/cpudeadline.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index ae4fbdc..a200b36 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -136,6 +136,10 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
 
 		WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
 
+		/* The heap tree is empty, just return. */
+		if (best_cpu == -1)
+			return 0;
+
 		if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) &&
 		    dl_time_before(dl_se->deadline, cpudl_maximum_dl(cp))) {
 			if (later_mask)
@@ -172,6 +176,13 @@ void cpudl_clear(struct cpudl *cp, int cpu)
 		 * This could happen if a rq_offline_dl is
 		 * called for a CPU without -dl tasks running.
 		 */
+	} else if (cp->size == 1){
+		/* Only one element in the heap, clear it. */
+		cp->elements[0].cpu = -1;
+		cp->elements[cpu].idx = IDX_INVALID;
+		cp->size = 0;
+
+		cpumask_set_cpu(cpu, cp->free_cpus);
 	} else {
 		new_cpu = cp->elements[cp->size - 1].cpu;
 		cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
@@ -267,6 +278,9 @@ int cpudl_init(struct cpudl *cp)
 	for_each_possible_cpu(i)
 		cp->elements[i].idx = IDX_INVALID;
 
+	/* Mark heap as initially empty. */
+	cp->elements[0].cpu = -1;
+
 	return 0;
 }
 
-- 
1.9.1