From 738664c5270d93720c11717f55c288b1d5d3dae5 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 20 May 2025 11:19:30 +0200 Subject: [PATCH] FROMGIT: sched/deadline: Less agressive dl_server handling Chris reported that commit 5f6bd380c7bd ("sched/rt: Remove default bandwidth control") caused a significant dip in his favourite benchmark of the day. Simply disabling dl_server cured things. His workload hammers the 0->1, 1->0 transitions, and the dl_server_{start,stop}() overhead kills it -- fairly obviously a bad idea in hind sight and all that. Change things around to only disable the dl_server when there has not been a fair task around for a whole period. Since the default period is 1 second, this ensures the benchmark never trips this, overhead gone. Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server") Reported-by: Chris Mason Signed-off-by: Peter Zijlstra (Intel) (cherry picked from commit 7bca60ce656978b01caafc4e2285272ae9631953 https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=sched/core) Link: https://lore.kernel.org/all/20250520101727.507378961@infradead.org/ Tested-by: K Prateek Nayak Change-Id: Iaa47846edcc4a06e87baf21fccfbd0cbdeaf2b7f Bug: 410614532 Bug: 422165470 Signed-off-by: Shaleen Agrawal [jstultz: Switched to FROMGIT] Signed-off-by: John Stultz --- include/linux/sched.h | 1 + kernel/sched/deadline.c | 31 +++++++++++++++++++++++++++---- 2 files changed, 28 insertions(+), 4 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 227da214e5b6..159cd50678be 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -689,6 +689,7 @@ struct sched_dl_entity { unsigned int dl_defer : 1; unsigned int dl_defer_armed : 1; unsigned int dl_defer_running : 1; + unsigned int dl_server_idle : 1; /* * Bandwidth enforcement timer. Each -deadline task has its diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 6751f056c8ab..a49b93ccbfc5 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1195,6 +1195,8 @@ static void __push_dl_task(struct rq *rq, struct rq_flags *rf) /* a defer timer will not be reset if the runtime consumed was < dl_server_min_res */ static const u64 dl_server_min_res = 1 * NSEC_PER_MSEC; +static bool dl_server_stopped(struct sched_dl_entity *dl_se); + static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_dl_entity *dl_se) { struct rq *rq = rq_of_dl_se(dl_se); @@ -1214,6 +1216,7 @@ static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_ if (!dl_se->server_has_tasks(dl_se)) { replenish_dl_entity(dl_se); + dl_server_stopped(dl_se); return HRTIMER_NORESTART; } @@ -1620,8 +1623,10 @@ void dl_server_update_idle_time(struct rq *rq, struct task_struct *p) 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_runtime) { + dl_se->dl_server_idle = 0; update_curr_dl_se(dl_se->rq, dl_se, delta_exec); + } } void dl_server_start(struct sched_dl_entity *dl_se) @@ -1644,7 +1649,7 @@ void dl_server_start(struct sched_dl_entity *dl_se) setup_new_dl_entity(dl_se); } - if (!dl_se->dl_runtime) + if (!dl_se->dl_runtime || dl_se->dl_server_active) return; dl_se->dl_server_active = 1; @@ -1653,7 +1658,7 @@ void dl_server_start(struct sched_dl_entity *dl_se) resched_curr(dl_se->rq); } -void dl_server_stop(struct sched_dl_entity *dl_se) +static void __dl_server_stop(struct sched_dl_entity *dl_se) { if (!dl_se->dl_runtime) return; @@ -1665,6 +1670,24 @@ void dl_server_stop(struct sched_dl_entity *dl_se) dl_se->dl_server_active = 0; } +static bool dl_server_stopped(struct sched_dl_entity *dl_se) +{ + if (!dl_se->dl_server_active) + return false; + + if (dl_se->dl_server_idle) { + __dl_server_stop(dl_se); + return true; + } + + dl_se->dl_server_idle = 1; + return false; +} + +void dl_server_stop(struct sched_dl_entity *dl_se) +{ +} + 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) @@ -2432,7 +2455,7 @@ again: if (dl_server(dl_se)) { p = dl_se->server_pick_task(dl_se); if (!p) { - if (dl_server_active(dl_se)) { + if (!dl_server_stopped(dl_se)) { dl_se->dl_yielded = 1; update_curr_dl_se(rq, dl_se, 0); }