From e636ffb9e31b4f7dde7fef5358669266b9ce02ec Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 20 Oct 2025 16:15:05 +0200 Subject: [PATCH] sched/deadline: Fix dl_server time accounting The dl_server time accounting code is a little odd. The normal scheduler pattern is to update curr before doing something, such that the old state is fully accounted before changing state. Notably, the dl_server_timer() needs to propagate the current time accounting since the current task could be ran by dl_server and thus this can affect dl_se->runtime. Similarly for dl_server_start(). And since the (deferred) dl_server wants idle time accounted, rework sched_idle_class time accounting to be more like all the others. Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20251020141130.GJ3245006@noisy.programming.kicks-ass.net --- kernel/sched/deadline.c | 40 +++++++++++++++------------------------- kernel/sched/fair.c | 9 ++------- kernel/sched/idle.c | 16 +++++++++++++++- kernel/sched/sched.h | 3 +-- 4 files changed, 33 insertions(+), 35 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 13112c680f922..ece25caf379cc 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1166,8 +1166,12 @@ static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_ sched_clock_tick(); update_rq_clock(rq); - if (!dl_se->dl_runtime) - return HRTIMER_NORESTART; + /* + * Make sure current has propagated its pending runtime into + * any relevant server through calling dl_server_update() and + * friends. + */ + rq->donor->sched_class->update_curr(rq); if (dl_se->dl_defer_armed) { /* @@ -1543,35 +1547,16 @@ throttle: * as time available for the fair server, avoiding a penalty for the * rt scheduler that did not consumed that time. */ -void dl_server_update_idle_time(struct rq *rq, struct task_struct *p) +void dl_server_update_idle(struct sched_dl_entity *dl_se, s64 delta_exec) { - s64 delta_exec; - - if (!rq->fair_server.dl_defer) - return; - - /* no need to discount more */ - if (rq->fair_server.runtime < 0) - return; - - delta_exec = rq_clock_task(rq) - p->se.exec_start; - if (delta_exec < 0) - return; - - rq->fair_server.runtime -= delta_exec; - - if (rq->fair_server.runtime < 0) { - rq->fair_server.dl_defer_running = 0; - rq->fair_server.runtime = 0; - } - - p->se.exec_start = rq_clock_task(rq); + if (dl_se->dl_server_active && dl_se->dl_runtime && dl_se->dl_defer) + update_curr_dl_se(dl_se->rq, dl_se, delta_exec); } void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec) { /* 0 runtime = fair server disabled */ - if (dl_se->dl_runtime) + if (dl_se->dl_server_active && dl_se->dl_runtime) update_curr_dl_se(dl_se->rq, dl_se, delta_exec); } @@ -1582,6 +1567,11 @@ void dl_server_start(struct sched_dl_entity *dl_se) if (!dl_server(dl_se) || dl_se->dl_server_active) return; + /* + * Update the current task to 'now'. + */ + rq->donor->sched_class->update_curr(rq); + if (WARN_ON_ONCE(!cpu_online(cpu_of(rq)))) return; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8d971d48669fe..b4617d6315496 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1212,8 +1212,7 @@ static void update_curr(struct cfs_rq *cfs_rq) * against fair_server such that it can account for this time * and possibly avoid running this period. */ - if (dl_server_active(&rq->fair_server)) - dl_server_update(&rq->fair_server, delta_exec); + dl_server_update(&rq->fair_server, delta_exec); } account_cfs_rq_runtime(cfs_rq, delta_exec); @@ -6961,12 +6960,8 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) h_nr_idle = 1; } - if (!rq_h_nr_queued && rq->cfs.h_nr_queued) { - /* Account for idle runtime */ - if (!rq->nr_running) - dl_server_update_idle_time(rq, rq->curr); + if (!rq_h_nr_queued && rq->cfs.h_nr_queued) dl_server_start(&rq->fair_server); - } /* At this point se is NULL and we are at root level*/ add_nr_running(rq, 1); diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 7fa0b593bcff7..1cb7a3d70e658 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -452,9 +452,11 @@ static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags) resched_curr(rq); } +static void update_curr_idle(struct rq *rq); + static void put_prev_task_idle(struct rq *rq, struct task_struct *prev, struct task_struct *next) { - dl_server_update_idle_time(rq, prev); + update_curr_idle(rq); scx_update_idle(rq, false, true); } @@ -496,6 +498,7 @@ dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags) */ static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued) { + update_curr_idle(rq); } static void switching_to_idle(struct rq *rq, struct task_struct *p) @@ -514,6 +517,17 @@ prio_changed_idle(struct rq *rq, struct task_struct *p, u64 oldprio) static void update_curr_idle(struct rq *rq) { + struct sched_entity *se = &rq->idle->se; + u64 now = rq_clock_task(rq); + s64 delta_exec; + + delta_exec = now - se->exec_start; + if (unlikely(delta_exec <= 0)) + return; + + se->exec_start = now; + + dl_server_update_idle(&rq->fair_server, delta_exec); } /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 5a3cf81c27be3..def9ab7b59d42 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -404,6 +404,7 @@ extern s64 dl_scaled_delta_exec(struct rq *rq, struct sched_dl_entity *dl_se, s6 * naturally thottled to once per period, avoiding high context switch * workloads from spamming the hrtimer program/cancel paths. */ +extern void dl_server_update_idle(struct sched_dl_entity *dl_se, s64 delta_exec); extern void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec); extern void dl_server_start(struct sched_dl_entity *dl_se); extern void dl_server_stop(struct sched_dl_entity *dl_se); @@ -411,8 +412,6 @@ extern void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq, 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); extern void fair_server_init(struct rq *rq); extern void __dl_server_attach_root(struct sched_dl_entity *dl_se, struct rq *rq); extern int dl_server_apply_params(struct sched_dl_entity *dl_se, -- 2.47.3