Commit c3856c9c authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched/fair: Cleanup in migrate_degrades_locality() to improve readability 



migrate_degrade_locality() would return {1, 0, -1} respectively to
indicate that migration would degrade-locality, would improve
locality, would be ambivalent to locality improvements.

This patch improves readability by changing the return value to mean:
* Any positive value degrades locality
* 0 migration doesn't affect locality
* Any negative value improves locality

[Swapnil: Fixed comments around code and wrote commit log]

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Not-yet-signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarSwapnil Sapkal <swapnil.sapkal@amd.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241220063224.17767-3-swapnil.sapkal@amd.com
parent a430d99e

kernel/sched/fair.c

+21 −20
Original line number Diff line number Diff line
@@ -9329,43 +9329,43 @@ static int task_hot(struct task_struct *p, struct lb_env *env) 


#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.

 * Returns a positive value, if task migration degrades locality.

 * Returns 0, if task migration is not affected by locality.

 * Returns a negative value, if task migration improves locality i.e migration preferred.

 */

static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)

static long 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 0;



	if (!p->numa_faults || !(env->sd->flags & SD_NUMA))

		return -1;

		return 0;



	src_nid = cpu_to_node(env->src_cpu);

	dst_nid = cpu_to_node(env->dst_cpu);



	if (src_nid == dst_nid)

		return -1;

		return 0;



	/* 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;

		else

			return -1;

			return 0;

	}



	/* Encourage migration to the preferred node. */

	if (dst_nid == p->numa_preferred_nid)

		return 0;

		return -1;



	/* Leaving a core idle is often worse than degrading locality. */

	if (env->idle == CPU_IDLE)

		return -1;

		return 0;



	dist = node_distance(src_nid, dst_nid);

	if (numa_group) {
@@ -9376,14 +9376,14 @@ 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 src_weight - dst_weight;

}



#else

static inline int migrate_degrades_locality(struct task_struct *p,

static inline long migrate_degrades_locality(struct task_struct *p,

					     struct lb_env *env)

{

	return -1;

	return 0;

}

#endif
@@ -9393,7 +9393,7 @@ 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;

	long degrades, hot;



	lockdep_assert_rq_held(env->src_rq);

	if (p->sched_task_hot)
@@ -9468,13 +9468,14 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) 
	if (env->flags & LBF_ACTIVE_LB)

		return 1;



	tsk_cache_hot = migrate_degrades_locality(p, env);

	if (tsk_cache_hot == -1)

		tsk_cache_hot = task_hot(p, env);

	degrades = migrate_degrades_locality(p, env);

	if (!degrades)

		hot = task_hot(p, env);

	else

		hot = degrades > 0;



	if (tsk_cache_hot <= 0 ||

	    env->sd->nr_balance_failed > env->sd->cache_nice_tries) {

		if (tsk_cache_hot == 1)

	if (!hot || env->sd->nr_balance_failed > env->sd->cache_nice_tries) {

		if (hot)

			p->sched_task_hot = 1;

		return 1;

	}