Commit ca1e8eed authored by Gabriele Monaco's avatar Gabriele Monaco Committed by Peter Zijlstra
Browse files

sched/deadline: Fix server stopping with runnable tasks 



The deadline server can currently stop due to idle although fair tasks
are runnable. This happens essentially when:

 * the server is set to idle, a task wakes up, the server stops
 * a task wakes up, the server sets itself to idle and stops right away

Address both cases by clearing the server idle flag whenever a fair task
wakes up and accounting also for pending tasks in the definition of idle.

Fixes: f5a538c0 ("sched/deadline: Fix dl_server stop condition")
Signed-off-by: default avatarGabriele Monaco <gmonaco@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260113085159.114226-3-gmonaco@redhat.com
parent 1e0a2ba7

kernel/sched/deadline.c

+9 −4
Original line number Diff line number Diff line
@@ -1420,7 +1420,7 @@ update_stats_dequeue_dl(struct dl_rq *dl_rq, struct sched_dl_entity *dl_se, int 


static void update_curr_dl_se(struct rq *rq, struct sched_dl_entity *dl_se, s64 delta_exec)

{

	bool idle = rq->curr == rq->idle;

	bool idle = idle_rq(rq);

	s64 scaled_delta_exec;



	if (unlikely(delta_exec <= 0)) {
@@ -1604,7 +1604,7 @@ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec) 
 * |   |                                | <---+    |

 * |   +--------------------------------+          |

 * |     |              ^         ^       2        |

 * |     | 7            | 2   +--------------------+

 * |     | 7            | 2, 1    +----------------+

 * |     v              |

 * |   +-------------+  |

 * +-- | C:idle-wait | -+
@@ -1649,8 +1649,11 @@ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec) 
 *   dl_defer_idle = 0

 *

 *

 * [1] A->B, A->D

 * [1] A->B, A->D, C->B

 * dl_server_start()

 *   dl_defer_idle = 0;

 *   if (dl_server_active)

 *     return; // [B]

 *   dl_server_active = 1;

 *   enqueue_dl_entity()

 *     update_dl_entity(WAKEUP)
@@ -1759,6 +1762,7 @@ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec) 
 *   "B:zero_laxity-wait" -> "C:idle-wait"        [label="7:dl_server_update_idle"]

 *   "B:zero_laxity-wait" -> "D:running"          [label="3:dl_server_timer"]

 *   "C:idle-wait" -> "A:init"                    [label="8:dl_server_timer"]

 *   "C:idle-wait" -> "B:zero_laxity-wait"        [label="1:dl_server_start"]

 *   "C:idle-wait" -> "B:zero_laxity-wait"        [label="2:dl_server_update"]

 *   "C:idle-wait" -> "C:idle-wait"               [label="7:dl_server_update_idle"]

 *   "D:running" -> "A:init"                      [label="4:pick_task_dl"]
@@ -1784,6 +1788,7 @@ void dl_server_start(struct sched_dl_entity *dl_se) 
{

	struct rq *rq = dl_se->rq;



	dl_se->dl_defer_idle = 0;

	if (!dl_server(dl_se) || dl_se->dl_server_active)

		return;