sched/deadline: Document dl_server (2614069c) · Commits · git / linux-net

kernel/sched/deadline.c

+194 −0

Original line number	Diff line number	Diff line
		@@ -1595,6 +1595,200 @@ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec)
		update_curr_dl_se(dl_se->rq, dl_se, delta_exec);
		}

		/*
		* dl_server && dl_defer:
		*
		* 6
		* +--------------------+
		* v \|
		* +-------------+ 4 +-----------+ 5 +------------------+
		* +-> \| A:init \| <--- \| D:running \| -----> \| E:replenish-wait \|
		* \| +-------------+ +-----------+ +------------------+
		* \| \| \| 1 ^ ^ \|
		* \| \| 1 +----------+ \| 3 \|
		* \| v \| \|
		* \| +--------------------------------+ 2 \|
		* \| \| \| ----+ \|
		* \| 8 \| B:zero_laxity-wait \| \| \|
		* \| \| \| <---+ \|
		* \| +--------------------------------+ \|
		* \| \| ^ ^ 2 \|
		* \| \| 7 \| 2 +--------------------+
		* \| v \|
		* \| +-------------+ \|
		* +-- \| C:idle-wait \| -+
		* +-------------+
		* ^ 7 \|
		* +---------+
		*
		*
		* [A] - init
		* dl_server_active = 0
		* dl_throttled = 0
		* dl_defer_armed = 0
		* dl_defer_running = 0/1
		* dl_defer_idle = 0
		*
		* [B] - zero_laxity-wait
		* dl_server_active = 1
		* dl_throttled = 1
		* dl_defer_armed = 1
		* dl_defer_running = 0
		* dl_defer_idle = 0
		*
		* [C] - idle-wait
		* dl_server_active = 1
		* dl_throttled = 1
		* dl_defer_armed = 1
		* dl_defer_running = 0
		* dl_defer_idle = 1
		*
		* [D] - running
		* dl_server_active = 1
		* dl_throttled = 0
		* dl_defer_armed = 0
		* dl_defer_running = 1
		* dl_defer_idle = 0
		*
		* [E] - replenish-wait
		* dl_server_active = 1
		* dl_throttled = 1
		* dl_defer_armed = 0
		* dl_defer_running = 1
		* dl_defer_idle = 0
		*
		*
		* [1] A->B, A->D
		* dl_server_start()
		* dl_server_active = 1;
		* enqueue_dl_entity()
		* update_dl_entity(WAKEUP)
		* if (!dl_defer_running)
		* dl_defer_armed = 1;
		* dl_throttled = 1;
		* if (dl_throttled && start_dl_timer())
		* return; // [B]
		* __enqueue_dl_entity();
		* // [D]
		*
		* // deplete server runtime from client-class
		* [2] B->B, C->B, E->B
		* dl_server_update()
		* update_curr_dl_se() // idle = false
		* if (dl_defer_idle)
		* dl_defer_idle = 0;
		* if (dl_defer && dl_throttled && dl_runtime_exceeded())
		* dl_defer_running = 0;
		* hrtimer_try_to_cancel(); // stop timer
		* replenish_dl_new_period()
		* // fwd period
		* dl_throttled = 1;
		* dl_defer_armed = 1;
		* start_dl_timer(); // restart timer
		* // [B]
		*
		* // timer actually fires means we have runtime
		* [3] B->D
		* dl_server_timer()
		* if (dl_defer_armed)
		* dl_defer_running = 1;
		* enqueue_dl_entity(REPLENISH)
		* replenish_dl_entity()
		* // fwd period
		* if (dl_throttled)
		* dl_throttled = 0;
		* if (dl_defer_armed)
		* dl_defer_armed = 0;
		* __enqueue_dl_entity();
		* // [D]
		*
		* // schedule server
		* [4] D->A
		* pick_task_dl()
		* p = server_pick_task();
		* if (!p)
		* dl_server_stop()
		* dequeue_dl_entity();
		* hrtimer_try_to_cancel();
		* dl_defer_armed = 0;
		* dl_throttled = 0;
		* dl_server_active = 0;
		* // [A]
		* return p;
		*
		* // server running
		* [5] D->E
		* update_curr_dl_se()
		* if (dl_runtime_exceeded())
		* dl_throttled = 1;
		* dequeue_dl_entity();
		* start_dl_timer();
		* // [E]
		*
		* // server replenished
		* [6] E->D
		* dl_server_timer()
		* enqueue_dl_entity(REPLENISH)
		* replenish_dl_entity()
		* fwd-period
		* if (dl_throttled)
		* dl_throttled = 0;
		* __enqueue_dl_entity();
		* // [D]
		*
		* // deplete server runtime from idle
		* [7] B->C, C->C
		* dl_server_update_idle()
		* update_curr_dl_se() // idle = true
		* if (dl_defer && dl_throttled && dl_runtime_exceeded())
		* if (dl_defer_idle)
		* return;
		* dl_defer_running = 0;
		* hrtimer_try_to_cancel();
		* replenish_dl_new_period()
		* // fwd period
		* dl_throttled = 1;
		* dl_defer_armed = 1;
		* dl_defer_idle = 1;
		* start_dl_timer(); // restart timer
		* // [C]
		*
		* // stop idle server
		* [8] C->A
		* dl_server_timer()
		* if (dl_defer_idle)
		* dl_server_stop();
		* // [A]
		*
		*
		* digraph dl_server {
		* "A:init" -> "B:zero_laxity-wait" [label="1:dl_server_start"]
		* "A:init" -> "D:running" [label="1:dl_server_start"]
		* "B:zero_laxity-wait" -> "B:zero_laxity-wait" [label="2:dl_server_update"]
		* "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="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"]
		* "D:running" -> "E:replenish-wait" [label="5:update_curr_dl_se"]
		* "E:replenish-wait" -> "B:zero_laxity-wait" [label="2:dl_server_update"]
		* "E:replenish-wait" -> "D:running" [label="6:dl_server_timer"]
		* }
		*
		*
		* Notes:
		*
		* - When there are fair tasks running the most likely loop is [2]->[2].
		* the dl_server never actually runs, the timer never fires.
		*
		* - When there is actual fair starvation; the timer fires and starts the
		* dl_server. This will then throttle and replenish like a normal DL
		* task. Notably it will not 'defer' again.
		*
		* - When idle it will push the actication forward once, and then wait
		* for the timer to hit or a non-idle update to restart things.
		*/
		void dl_server_start(struct sched_dl_entity *dl_se)
		{
		struct rq *rq = dl_se->rq;