Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Received-SPF: Pass (protection.outlook.com: domain of amd.com designates
 165.204.84.17 as permitted sender) receiver=protection.outlook.com;
 client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C
From:   Swapnil Sapkal <swapnil.sapkal@amd.com>
To:     <mingo@redhat.com>, <peterz@infradead.org>,
        <juri.lelli@redhat.com>, <vincent.guittot@linaro.org>
CC:     <dietmar.eggemann@arm.com>, <rostedt@goodmis.org>,
        <bsegall@google.com>, <mgorman@suse.de>, <bristot@redhat.com>,
        <vschneid@redhat.com>, <iamjoonsoo.kim@lge.com>,
        <linux-kernel@vger.kernel.org>, <gautham.shenoy@amd.com>,
        <kprateek.nayak@amd.com>, <wyes.karny@amd.com>,
        Swapnil Sapkal <swapnil.sapkal@amd.com>
Subject: [PATCH 2/2] sched/fair: Cleanup in migrate_degrades_locality() to improve readability
Date:   Wed, 14 Jun 2023 10:22:24 +0000
Message-ID: <20230614102224.12555-3-swapnil.sapkal@amd.com>
In-Reply-To: <20230614102224.12555-1-swapnil.sapkal@amd.com>
References: <20230614102224.12555-1-swapnil.sapkal@amd.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Jun 2023 10:23:40.7175
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 41445e9b-1dd1-4537-a9a6-08db6cc16c83
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com]
X-MS-Exchange-CrossTenant-AuthSource: CY4PEPF0000EE3A.namprd03.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB8739
X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,
        T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=no autolearn_force=no
        version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

The migrate_degrades_locality() returns tristate value whether
the migration will improve locality, degrades locality or no
impact. Handle this return values with enum to improve the
readability.

Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
---
 kernel/sched/fair.c | 69 +++++++++++++++++++++++++++++----------------
 1 file changed, 44 insertions(+), 25 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9a8e5dcbe7e6..06813ce5356e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8443,45 +8443,52 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 	return delta < (s64)sysctl_sched_migration_cost;
 }
 
+enum migration_impact {
+	/* if task migration is not affected by locality */
+	no_change = -1,
+
+	/* if task migration improves locality i.e migration preferred */
+	improves_locality = 0,
+
+	/* if task migration degrades locality */
+	degrades_locality = 1
+};
+
 #ifdef CONFIG_NUMA_BALANCING
-/*
- * Returns 1, if task migration degrades locality
- * Returns 0, if task migration improves locality i.e migration preferred.
- * Returns -1, if task migration is not affected by locality.
- */
-static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
+static enum migration_impact
+migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 {
 	struct numa_group *numa_group = rcu_dereference(p->numa_group);
 	unsigned long src_weight, dst_weight;
 	int src_nid, dst_nid, dist;
 
 	if (!static_branch_likely(&sched_numa_balancing))
-		return -1;
+		return no_change;
 
 	if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
-		return -1;
+		return no_change;
 
 	src_nid = cpu_to_node(env->src_cpu);
 	dst_nid = cpu_to_node(env->dst_cpu);
 
 	if (src_nid == dst_nid)
-		return -1;
+		return no_change;
 
 	/* Migrating away from the preferred node is always bad. */
 	if (src_nid == p->numa_preferred_nid) {
 		if (env->src_rq->nr_running > env->src_rq->nr_preferred_running)
-			return 1;
+			return degrades_locality;
 		else
-			return -1;
+			return no_change;
 	}
 
 	/* Encourage migration to the preferred node. */
 	if (dst_nid == p->numa_preferred_nid)
-		return 0;
+		return improves_locality;
 
 	/* Leaving a core idle is often worse than degrading locality. */
 	if (env->idle == CPU_IDLE)
-		return -1;
+		return no_change;
 
 	dist = node_distance(src_nid, dst_nid);
 	if (numa_group) {
@@ -8492,14 +8499,14 @@ static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 		dst_weight = task_weight(p, dst_nid, dist);
 	}
 
-	return dst_weight < src_weight;
+	return (dst_weight < src_weight) ? degrades_locality : improves_locality;
 }
 
 #else
-static inline int migrate_degrades_locality(struct task_struct *p,
-					     struct lb_env *env)
+static inline enum migration_impact
+migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 {
-	return -1;
+	return no_change;
 }
 #endif
 
@@ -8509,7 +8516,7 @@ static inline int migrate_degrades_locality(struct task_struct *p,
 static
 int can_migrate_task(struct task_struct *p, struct lb_env *env, int *tsk_cache_hot)
 {
-	int degrades_locality;
+	enum migration_impact migration_impact;
 
 	lockdep_assert_rq_held(env->src_rq);
 
@@ -8578,18 +8585,30 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env, int *tsk_cache_h
 	if (env->flags & LBF_ACTIVE_LB)
 		return 1;
 
-	degrades_locality = migrate_degrades_locality(p, env);
-	if (degrades_locality == -1)
+	migration_impact = migrate_degrades_locality(p, env);
+
+	switch (migration_impact) {
+	case no_change:
 		*tsk_cache_hot = task_hot(p, env);
-	else
-		*tsk_cache_hot = degrades_locality;
+		break;
+
+	case degrades_locality:
+		*tsk_cache_hot = 1;
+		break;
+
+	case improves_locality:
+		*tsk_cache_hot = 0;
+		break;
+	}
+
+	if (!(*tsk_cache_hot))
+		return 1;
 
 	/*
-	 * Can migrate a hot task only after the attempts to reach balance
+	 * Can migrate a task only after the attempts to reach balance
 	 * without the task have exceeded the cache_nice_tries threshold.
 	 */
-	if (!(*tsk_cache_hot) ||
-		env->sd->nr_balance_failed > env->sd->cache_nice_tries)
+	if (env->sd->nr_balance_failed > env->sd->cache_nice_tries)
 		return 1;
 
 	schedstat_inc(p->stats.nr_failed_migrations_hot);
-- 
2.34.1