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From:   Luca Abeni <luca.abeni@santannapisa.it>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        "Paul E . McKenney" <paulmck@linux.ibm.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Quentin Perret <quentin.perret@arm.com>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Patrick Bellasi <patrick.bellasi@arm.com>,
        Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
        luca abeni <luca.abeni@santannapisa.it>
Subject: [RFC PATCH 6/6] sched/dl: Try not to select a too fast core
Date:   Mon,  6 May 2019 06:48:36 +0200
Message-Id: <20190506044836.2914-7-luca.abeni@santannapisa.it>
In-Reply-To: <20190506044836.2914-1-luca.abeni@santannapisa.it>
References: <20190506044836.2914-1-luca.abeni@santannapisa.it>
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From: luca abeni <luca.abeni@santannapisa.it>

When a task can fit on multiple CPU cores, try to select the slowest
core that is able to properly serve the task. This avoids useless
future migrations, leaving the "fast cores" idle for more heavyweight
tasks.

Signed-off-by: luca abeni <luca.abeni@santannapisa.it>
---
 kernel/sched/cpudeadline.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 2a4ac7b529b7..897ed71af515 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -143,17 +143,24 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
 	       struct cpumask *later_mask)
 {
 	const struct sched_dl_entity *dl_se = &p->dl;
+	struct cpumask tmp_mask;
 
 	if (later_mask &&
-	    cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
+	    cpumask_and(&tmp_mask, cp->free_cpus, &p->cpus_allowed)) {
 		int cpu, max_cpu = -1;
-		u64 max_cap = 0;
+		u64 max_cap = 0, min_cap = SCHED_CAPACITY_SCALE * SCHED_CAPACITY_SCALE;
 
-		for_each_cpu(cpu, later_mask) {
+		cpumask_clear(later_mask);
+		for_each_cpu(cpu, &tmp_mask) {
 			u64 cap;
 
-			if (!dl_task_fit(&p->dl, cpu, &cap))
-				cpumask_clear_cpu(cpu, later_mask);
+			if (dl_task_fit(&p->dl, cpu, &cap) && (cap <= min_cap)) {
+				if (cap < min_cap) {
+					min_cap = cap;
+					cpumask_clear(later_mask);
+				}
+				cpumask_set_cpu(cpu, later_mask);
+			}
 
 			if (cap > max_cap) {
 				max_cap = cap;
-- 
2.20.1