sched: Report the different kinds of imbalances in /proc/schedstat

JIRA: https://issues.redhat.com/browse/RHEL-23495

commit 3b2a793
Author: Swapnil Sapkal <swapnil.sapkal@amd.com>
Date:   Fri Dec 20 06:32:21 2024 +0000

    sched: Report the different kinds of imbalances in /proc/schedstat

    In /proc/schedstat, lb_imbalance reports the sum of imbalances
    discovered in sched domains with each call to sched_balance_rq(), which is
    not very useful because lb_imbalance does not mention whether the imbalance
    is due to load, utilization, nr_tasks or misfit_tasks. Remove this field
    from /proc/schedstat.

    Currently there is no field in /proc/schedstat to report different types
    of imbalances. Introduce new fields in /proc/schedstat to report the
    total imbalances in load, utilization, nr_tasks or misfit_tasks.

    Added fields to /proc/schedstat:
            - lb_imbalance_load: Total imbalance due to load.
            - lb_imbalance_util: Total imbalance due to utilization.
            - lb_imbalance_task: Total imbalance due to number of tasks.
            - lb_imbalance_misfit: Total imbalance due to misfit tasks.

    Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
    Link: https://lore.kernel.org/r/20241220063224.17767-4-swapnil.sapkal@amd.com

Signed-off-by: Phil Auld <pauld@redhat.com>

Author: auldp

include/linux/sched/topology.h

@@ -114,7 +114,10 @@ struct sched_domain {
 	unsigned int lb_count[CPU_MAX_IDLE_TYPES];
 	unsigned int lb_failed[CPU_MAX_IDLE_TYPES];
 	unsigned int lb_balanced[CPU_MAX_IDLE_TYPES];
-	unsigned int lb_imbalance[CPU_MAX_IDLE_TYPES];
+	unsigned int lb_imbalance_load[CPU_MAX_IDLE_TYPES];
+	unsigned int lb_imbalance_util[CPU_MAX_IDLE_TYPES];
+	unsigned int lb_imbalance_task[CPU_MAX_IDLE_TYPES];
+	unsigned int lb_imbalance_misfit[CPU_MAX_IDLE_TYPES];
 	unsigned int lb_gained[CPU_MAX_IDLE_TYPES];
 	unsigned int lb_hot_gained[CPU_MAX_IDLE_TYPES];
 	unsigned int lb_nobusyg[CPU_MAX_IDLE_TYPES];

kernel/sched/fair.c

@@ -11219,6 +11219,28 @@ static int should_we_balance(struct lb_env *env)
 	return group_balance_cpu(sg) == env->dst_cpu;
 }
 
+static void update_lb_imbalance_stat(struct lb_env *env, struct sched_domain *sd,
+				     enum cpu_idle_type idle)
+{
+	if (!schedstat_enabled())
+		return;
+
+	switch (env->migration_type) {
+	case migrate_load:
+		__schedstat_add(sd->lb_imbalance_load[idle], env->imbalance);
+		break;
+	case migrate_util:
+		__schedstat_add(sd->lb_imbalance_util[idle], env->imbalance);
+		break;
+	case migrate_task:
+		__schedstat_add(sd->lb_imbalance_task[idle], env->imbalance);
+		break;
+	case migrate_misfit:
+		__schedstat_add(sd->lb_imbalance_misfit[idle], env->imbalance);
+		break;
+	}
+}
+
 /*
  * Check this_cpu to ensure it is balanced within domain. Attempt to move
  * tasks if there is an imbalance.
@@ -11269,7 +11291,7 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
 
 	WARN_ON_ONCE(busiest == env.dst_rq);
 
-	schedstat_add(sd->lb_imbalance[idle], env.imbalance);
+	update_lb_imbalance_stat(&env, sd, idle);
 
 	env.src_cpu = busiest->cpu;
 	env.src_rq = busiest;

kernel/sched/stats.c

@@ -151,11 +151,14 @@ static int show_schedstat(struct seq_file *seq, void *v)
 			seq_printf(seq, "domain%d %*pb", dcount++,
 				   cpumask_pr_args(sched_domain_span(sd)));
 			for (itype = 0; itype < CPU_MAX_IDLE_TYPES; itype++) {
-				seq_printf(seq, " %u %u %u %u %u %u %u %u",
+				seq_printf(seq, " %u %u %u %u %u %u %u %u %u %u %u",
 				    sd->lb_count[itype],
 				    sd->lb_balanced[itype],
 				    sd->lb_failed[itype],
-				    sd->lb_imbalance[itype],
+				    sd->lb_imbalance_load[itype],
+				    sd->lb_imbalance_util[itype],
+				    sd->lb_imbalance_task[itype],
+				    sd->lb_imbalance_misfit[itype],
 				    sd->lb_gained[itype],
 				    sd->lb_hot_gained[itype],
 				    sd->lb_nobusyq[itype],