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sched/deadline: Initialize dl_servers after SMP 

dl-servers are currently initialized too early at boot when CPUs are not
fully up (only boot CPU is). This results in miscalculation of per
runqueue DEADLINE variables like extra_bw (which needs a stable CPU
count).

Move initialization of dl-servers later on after SMP has been
initialized and CPUs are all online, so that CPU count is stable and
DEADLINE variables can be computed correctly.

Fixes: d741f297bc ("sched/fair: Fair server interface")
Reported-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk> # nuc & rock5b
Link: https://lore.kernel.org/r/20250627115118.438797-2-juri.lelli@redhat.com
pull/1309/head
Juri Lelli 2025-06-27 13:51:14 +02:00 committed by Peter Zijlstra
parent 2885daf470
commit 9f239df555
3 changed files with 33 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/sched/core.c
View File

@ -8371,6 +8371,8 @@ void __init sched_init_smp(void)
init_sched_rt_class();
init_sched_dl_class();
sched_init_dl_servers();
sched_smp_initialized = true;
}

48
kernel/sched/deadline.c
View File

@ -761,6 +761,8 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
struct rq *rq = rq_of_dl_rq(dl_rq);
update_rq_clock(rq);
WARN_ON(is_dl_boosted(dl_se));
WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
@ -1585,23 +1587,7 @@ void dl_server_start(struct sched_dl_entity *dl_se)
{
struct rq *rq = dl_se->rq;
/*
* XXX: the apply do not work fine at the init phase for the
* fair server because things are not yet set. We need to improve
* this before getting generic.
*/
if (!dl_server(dl_se)) {
u64 runtime = 50 * NSEC_PER_MSEC;
u64 period = 1000 * NSEC_PER_MSEC;
dl_server_apply_params(dl_se, runtime, period, 1);
dl_se->dl_server = 1;
dl_se->dl_defer = 1;
setup_new_dl_entity(dl_se);
}
if (!dl_se->dl_runtime || dl_se->dl_server_active)
if (!dl_server(dl_se) || dl_se->dl_server_active)
return;
dl_se->dl_server_active = 1;
@ -1612,7 +1598,7 @@ void dl_server_start(struct sched_dl_entity *dl_se)
void dl_server_stop(struct sched_dl_entity *dl_se)
{
if (!dl_se->dl_runtime)
if (!dl_server(dl_se) || !dl_server_active(dl_se))
return;
dequeue_dl_entity(dl_se, DEQUEUE_SLEEP);
@ -1645,6 +1631,32 @@ void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
dl_se->server_pick_task = pick_task;
}
void sched_init_dl_servers(void)
{
int cpu;
struct rq *rq;
struct sched_dl_entity *dl_se;
for_each_online_cpu(cpu) {
u64 runtime = 50 * NSEC_PER_MSEC;
u64 period = 1000 * NSEC_PER_MSEC;
rq = cpu_rq(cpu);
guard(rq_lock_irq)(rq);
dl_se = &rq->fair_server;
WARN_ON(dl_server(dl_se));
dl_server_apply_params(dl_se, runtime, period, 1);
dl_se->dl_server = 1;
dl_se->dl_defer = 1;
setup_new_dl_entity(dl_se);
}
}
void __dl_server_attach_root(struct sched_dl_entity *dl_se, struct rq *rq)
{
u64 new_bw = dl_se->dl_bw;

1
kernel/sched/sched.h
View File

@ -385,6 +385,7 @@ extern void dl_server_stop(struct sched_dl_entity *dl_se);
extern void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
dl_server_has_tasks_f has_tasks,
dl_server_pick_f pick_task);
extern void sched_init_dl_servers(void);
extern void dl_server_update_idle_time(struct rq *rq,
struct task_struct *p);