sched/fair: Don't double balance_interval for migrate_misfit

It is not necessarily an indication of the system being busy and
requires a backoff of the load balancer activities. But pushing it high
could mean generally delaying other misfit activities or other type of
imbalances.

Also don't pollute nr_balance_failed because of misfit failures. The
value is used for enabling cache hot migration and in migrate_util/load
types. None of which should be impacted (skewed) by misfit failures.

Signed-off-by: Qais Yousef <qyousef@layalina.io>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240324004552.999936-5-qyousef@layalina.io

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c47c4f2e28f7fd194b200ff411c0325e43eac33b..dbf4f1c442594071de12c768e05f4f65b89d4d54 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11449,8 +11449,12 @@ more_balance:
                 * We do not want newidle balance, which can be very
                 * frequent, pollute the failure counter causing
                 * excessive cache_hot migrations and active balances.
+                *
+                * Similarly for migration_misfit which is not related to
+                * load/util migration, don't pollute nr_balance_failed.
                 */
-               if (idle != CPU_NEWLY_IDLE)
+               if (idle != CPU_NEWLY_IDLE &&
+                   env.migration_type != migrate_misfit)
                        sd->nr_balance_failed++;
 
                if (need_active_balance(&env)) {
@@ -11533,8 +11537,13 @@ out_one_pinned:
         * repeatedly reach this code, which would lead to balance_interval
         * skyrocketing in a short amount of time. Skip the balance_interval
         * increase logic to avoid that.
+        *
+        * Similarly misfit migration which is not necessarily an indication of
+        * the system being busy and requires lb to backoff to let it settle
+        * down.
         */
-       if (env.idle == CPU_NEWLY_IDLE)
+       if (env.idle == CPU_NEWLY_IDLE ||
+           env.migration_type == migrate_misfit)
                goto out;
 
        /* tune up the balancing interval */