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sched/fair: Revert max_newidle_lb_cost bump

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Many people reported regressions on their database workloads due to:

  155213a2ae ("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
This commit is contained in:
Peter Zijlstra 2025-11-07 17:01:20 +01:00
parent e837456fdc
commit d206fbad93
1 changed files with 3 additions and 16 deletions
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19
kernel/sched/fair.c
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@ -12230,14 +12230,8 @@ 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)) {
/*
@ -12920,17 +12914,10 @@ 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);
}
/*