Commit 9f239df5 authored by Juri Lelli's avatar Juri Lelli Committed by Peter Zijlstra
Browse files

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: d741f297 ("sched/fair: Fair server interface")
Reported-by: default avatarMarcel Ziswiler <marcel.ziswiler@codethink.co.uk>
Signed-off-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarWaiman 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
parent 2885daf4

kernel/sched/core.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

}

kernel/sched/deadline.c

+30 −18
Original line number Diff line number Diff line
@@ -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;

kernel/sched/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -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);