Commit 7ef7145a authored by Ingo Molnar's avatar Ingo Molnar
Browse files

sched/nohz: Update idle load-balancing (ILB) comments 



 - Fix incorrect/misleading comments,

 - clarify some others,

 - fix typos & grammar,

 - and use more consistent style throughout.

Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lore.kernel.org/r/20231006102518.2452758-2-mingo@kernel.org
parent bc87127a

kernel/sched/fair.c

+16 −14
Original line number Diff line number Diff line
@@ -11503,14 +11503,15 @@ static inline int on_null_domain(struct rq *rq) 


#ifdef CONFIG_NO_HZ_COMMON

/*

 * idle load balancing details

 * - When one of the busy CPUs notice that there may be an idle rebalancing

 * NOHZ idle load balancing (ILB) details:

 *

 * - When one of the busy CPUs notices that there may be an idle rebalancing

 *   needed, they will kick the idle load balancer, which then does idle

 *   load balancing for all the idle CPUs.

 * - HK_TYPE_MISC CPUs are used for this task, because HK_TYPE_SCHED not set

 *

 * - HK_TYPE_MISC CPUs are used for this task, because HK_TYPE_SCHED is not set

 *   anywhere yet.

 */



static inline int find_new_ilb(void)

{

	int ilb;
@@ -11531,8 +11532,10 @@ static inline int find_new_ilb(void) 
}



/*

 * Kick a CPU to do the nohz balancing, if it is time for it. We pick any

 * idle CPU in the HK_TYPE_MISC housekeeping set (if there is one).

 * Kick a CPU to do the NOHZ balancing, if it is time for it, via a cross-CPU

 * SMP function call (IPI).

 *

 * We pick the first idle CPU in the HK_TYPE_MISC housekeeping set (if there is one).

 */

static void kick_ilb(unsigned int flags)

{
@@ -11560,7 +11563,7 @@ static void kick_ilb(unsigned int flags) 


	/*

	 * This way we generate an IPI on the target CPU which

	 * is idle. And the softirq performing nohz idle load balance

	 * is idle, and the softirq performing NOHZ idle load balancing

	 * will be run before returning from the IPI.

	 */

	smp_call_function_single_async(ilb_cpu, &cpu_rq(ilb_cpu)->nohz_csd);
@@ -11589,7 +11592,7 @@ static void nohz_balancer_kick(struct rq *rq) 


	/*

	 * None are in tickless mode and hence no need for NOHZ idle load

	 * balancing.

	 * balancing:

	 */

	if (likely(!atomic_read(&nohz.nr_cpus)))

		return;
@@ -11611,9 +11614,8 @@ static void nohz_balancer_kick(struct rq *rq) 
	sd = rcu_dereference(rq->sd);

	if (sd) {

		/*

		 * If there's a CFS task and the current CPU has reduced

		 * capacity; kick the ILB to see if there's a better CPU to run

		 * on.

		 * If there's a runnable CFS task and the current CPU has reduced

		 * capacity, kick the ILB to see if there's a better CPU to run on:

		 */

		if (rq->cfs.h_nr_running >= 1 && check_cpu_capacity(rq, sd)) {

			flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
@@ -11665,11 +11667,11 @@ static void nohz_balancer_kick(struct rq *rq) 
	if (sds) {

		/*

		 * If there is an imbalance between LLC domains (IOW we could

		 * increase the overall cache use), we need some less-loaded LLC

		 * domain to pull some load. Likewise, we may need to spread

		 * increase the overall cache utilization), we need a less-loaded LLC

		 * domain to pull some load from. Likewise, we may need to spread

		 * load within the current LLC domain (e.g. packed SMT cores but

		 * other CPUs are idle). We can't really know from here how busy

		 * the others are - so just get a nohz balance going if it looks

		 * the others are - so just get a NOHZ balance going if it looks

		 * like this LLC domain has tasks we could move.

		 */

		nr_busy = atomic_read(&sds->nr_busy_cpus);