linux-kernel - [RFC PATCH 1/3] sched/deadline: refactor cpu heap code

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Date:	Sun, 14 Aug 2016 16:27:06 +0200
From:	Tommaso Cucinotta <tommaso.cucinotta@...up.it>
To:	Luca Abeni <luca.abeni@...tn.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-dl@...is.sssup.it,
	Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
	Juri Lelli <juri.lelli@....com>
Subject: [RFC PATCH 1/3] sched/deadline: refactor cpu heap code

1. heapify up factored out in new dedicated function heapify_up()
   (avoids repetition of same code)
2. call to cpudl_change_key() replaced with heapify_up() when
   cpudl_set actually inserts a new node in the heap
3. cpudl_change_key() replaced with heapify() that heapifies up
   or down as needed.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@....com>
Cc: Luca Abeni <luca.abeni@...tn.it>
Reviewed-by: Luca Abeni <luca.abeni@...tn.it>
Reviewed-by: Juri Lelli <juri.lelli@....com>
Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@...up.it>
---
 kernel/sched/cpudeadline.c | 50 +++++++++++++++++++++-------------------------
 1 file changed, 23 insertions(+), 27 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index d418449..0acb0d4 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -41,7 +41,7 @@ static void cpudl_exchange(struct cpudl *cp, int a, int b)
 	swap(cp->elements[cpu_a].idx, cp->elements[cpu_b].idx);
 }
 
-static void cpudl_heapify(struct cpudl *cp, int idx)
+static void cpudl_heapify_down(struct cpudl *cp, int idx)
 {
 	int l, r, largest;
 
@@ -66,23 +66,24 @@ static void cpudl_heapify(struct cpudl *cp, int idx)
 	}
 }
 
-static void cpudl_change_key(struct cpudl *cp, int idx, u64 new_dl)
+static void cpudl_heapify_up(struct cpudl *cp, int idx)
 {
-	WARN_ON(idx == IDX_INVALID || !cpu_present(idx));
-
-	if (dl_time_before(new_dl, cp->elements[idx].dl)) {
-		cp->elements[idx].dl = new_dl;
-		cpudl_heapify(cp, idx);
-	} else {
-		cp->elements[idx].dl = new_dl;
-		while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
-					cp->elements[idx].dl)) {
-			cpudl_exchange(cp, idx, parent(idx));
-			idx = parent(idx);
-		}
+	while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
+			cp->elements[idx].dl)) {
+		cpudl_exchange(cp, idx, parent(idx));
+		idx = parent(idx);
 	}
 }
 
+static void cpudl_heapify(struct cpudl *cp, int idx)
+{
+	if (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
+				cp->elements[idx].dl))
+		cpudl_heapify_up(cp, idx);
+	else
+		cpudl_heapify_down(cp, idx);
+}
+
 static inline int cpudl_maximum(struct cpudl *cp)
 {
 	return cp->elements[0].cpu;
@@ -154,27 +155,22 @@ void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)
 		cp->size--;
 		cp->elements[new_cpu].idx = old_idx;
 		cp->elements[cpu].idx = IDX_INVALID;
-		while (old_idx > 0 && dl_time_before(
-				cp->elements[parent(old_idx)].dl,
-				cp->elements[old_idx].dl)) {
-			cpudl_exchange(cp, old_idx, parent(old_idx));
-			old_idx = parent(old_idx);
-		}
+		cpudl_heapify(cp, old_idx);
 		cpumask_set_cpu(cpu, cp->free_cpus);
-                cpudl_heapify(cp, old_idx);
 
 		goto out;
 	}
 
 	if (old_idx == IDX_INVALID) {
-		cp->size++;
-		cp->elements[cp->size - 1].dl = dl;
-		cp->elements[cp->size - 1].cpu = cpu;
-		cp->elements[cpu].idx = cp->size - 1;
-		cpudl_change_key(cp, cp->size - 1, dl);
+		int new_idx = cp->size++;
+		cp->elements[new_idx].dl = dl;
+		cp->elements[new_idx].cpu = cpu;
+		cp->elements[cpu].idx = new_idx;
+		cpudl_heapify_up(cp, new_idx);
 		cpumask_clear_cpu(cpu, cp->free_cpus);
 	} else {
-		cpudl_change_key(cp, old_idx, dl);
+		cp->elements[old_idx].dl = dl;
+		cpudl_heapify(cp, old_idx);
 	}
 
 out:
-- 
2.7.4