From: Peter Zijlstra <peterz@infradead.org>
commit d206fbad9328ddb68ebabd7cf7413392acd38081 upstream.
Many people reported regressions on their database workloads due to:
155213a2aed4 ("sched/fair: Bump sd->max_newidle_lb_cost when newidle balance fails")
For instance Adam Li reported a 6% regression on SpecJBB.
Conversely this will regress schbench again; on my machine from 2.22
Mrps/s down to 2.04 Mrps/s.
Reported-by: Joseph Salisbury <joseph.salisbury@oracle.com>
Reported-by: Adam Li <adamli@os.amperecomputing.com>
Reported-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reported-by: Hazem Mohamed Abuelfotoh <abuehaze@amazon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Chris Mason <clm@meta.com>
Link: https://lkml.kernel.org/r/20250626144017.1510594-2-clm@fb.com
Link: https://lkml.kernel.org/r/006c9df2-b691-47f1-82e6-e233c3f91faf@oracle.com
Link: https://patch.msgid.link/20251107161739.406147760@infradead.org
[ Ajay: Modified to apply on v6.6 ]
Signed-off-by: Ajay Kaher <ajay.kaher@broadcom.com>
---
kernel/sched/fair.c | 19 +++----------------
1 file changed, 3 insertions(+), 16 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7f23b866c..842d54a91 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11710,14 +11710,8 @@ static inline bool update_newidle_cost(struct sched_domain *sd, u64 cost)
/*
* Track max cost of a domain to make sure to not delay the
* next wakeup on the CPU.
- *
- * sched_balance_newidle() bumps the cost whenever newidle
- * balance fails, and we don't want things to grow out of
- * control. Use the sysctl_sched_migration_cost as the upper
- * limit, plus a litle extra to avoid off by ones.
*/
- sd->max_newidle_lb_cost =
- min(cost, sysctl_sched_migration_cost + 200);
+ sd->max_newidle_lb_cost = cost;
sd->last_decay_max_lb_cost = jiffies;
} else if (time_after(jiffies, sd->last_decay_max_lb_cost + HZ)) {
/*
@@ -12403,17 +12397,10 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
t1 = sched_clock_cpu(this_cpu);
domain_cost = t1 - t0;
+ update_newidle_cost(sd, domain_cost);
+
curr_cost += domain_cost;
t0 = t1;
-
- /*
- * Failing newidle means it is not effective;
- * bump the cost so we end up doing less of it.
- */
- if (!pulled_task)
- domain_cost = (3 * sd->max_newidle_lb_cost) / 2;
-
- update_newidle_cost(sd, domain_cost);
}
/*
--
2.40.4