mirror of https://github.com/torvalds/linux.git
sched/deadline: Document dl_server
Place the notes that resulted from going through the dl_server code in a comment. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Peter Zijlstra
parent
f5a538c07d
commit
2614069c59
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@ -1595,6 +1595,200 @@ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec)
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update_curr_dl_se(dl_se->rq, dl_se, delta_exec);
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}
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/*
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* dl_server && dl_defer:
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*
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* 6
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* +--------------------+
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* v |
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* +-------------+ 4 +-----------+ 5 +------------------+
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* +-> | A:init | <--- | D:running | -----> | E:replenish-wait |
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* | +-------------+ +-----------+ +------------------+
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* | | | 1 ^ ^ |
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* | | 1 +----------+ | 3 |
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* | v | |
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* | +--------------------------------+ 2 |
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* | | | ----+ |
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* | 8 | B:zero_laxity-wait | | |
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* | | | <---+ |
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* | +--------------------------------+ |
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* | | ^ ^ 2 |
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* | | 7 | 2 +--------------------+
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* | v |
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* | +-------------+ |
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* +-- | C:idle-wait | -+
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* +-------------+
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* ^ 7 |
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* +---------+
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*
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*
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* [A] - init
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* dl_server_active = 0
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* dl_throttled = 0
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* dl_defer_armed = 0
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* dl_defer_running = 0/1
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* dl_defer_idle = 0
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*
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* [B] - zero_laxity-wait
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* dl_server_active = 1
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* dl_throttled = 1
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* dl_defer_armed = 1
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* dl_defer_running = 0
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* dl_defer_idle = 0
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*
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* [C] - idle-wait
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* dl_server_active = 1
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* dl_throttled = 1
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* dl_defer_armed = 1
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* dl_defer_running = 0
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* dl_defer_idle = 1
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*
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* [D] - running
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* dl_server_active = 1
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* dl_throttled = 0
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* dl_defer_armed = 0
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* dl_defer_running = 1
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* dl_defer_idle = 0
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*
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* [E] - replenish-wait
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* dl_server_active = 1
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* dl_throttled = 1
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* dl_defer_armed = 0
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* dl_defer_running = 1
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* dl_defer_idle = 0
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*
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*
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* [1] A->B, A->D
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* dl_server_start()
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* dl_server_active = 1;
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* enqueue_dl_entity()
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* update_dl_entity(WAKEUP)
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* if (!dl_defer_running)
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* dl_defer_armed = 1;
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* dl_throttled = 1;
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* if (dl_throttled && start_dl_timer())
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* return; // [B]
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* __enqueue_dl_entity();
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* // [D]
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*
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* // deplete server runtime from client-class
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* [2] B->B, C->B, E->B
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* dl_server_update()
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* update_curr_dl_se() // idle = false
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* if (dl_defer_idle)
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* dl_defer_idle = 0;
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* if (dl_defer && dl_throttled && dl_runtime_exceeded())
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* dl_defer_running = 0;
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* hrtimer_try_to_cancel(); // stop timer
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* replenish_dl_new_period()
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* // fwd period
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* dl_throttled = 1;
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* dl_defer_armed = 1;
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* start_dl_timer(); // restart timer
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* // [B]
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*
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* // timer actually fires means we have runtime
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* [3] B->D
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* dl_server_timer()
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* if (dl_defer_armed)
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* dl_defer_running = 1;
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* enqueue_dl_entity(REPLENISH)
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* replenish_dl_entity()
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* // fwd period
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* if (dl_throttled)
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* dl_throttled = 0;
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* if (dl_defer_armed)
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* dl_defer_armed = 0;
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* __enqueue_dl_entity();
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* // [D]
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*
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* // schedule server
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* [4] D->A
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* pick_task_dl()
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* p = server_pick_task();
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* if (!p)
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* dl_server_stop()
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* dequeue_dl_entity();
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* hrtimer_try_to_cancel();
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* dl_defer_armed = 0;
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* dl_throttled = 0;
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* dl_server_active = 0;
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* // [A]
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* return p;
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*
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* // server running
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* [5] D->E
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* update_curr_dl_se()
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* if (dl_runtime_exceeded())
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* dl_throttled = 1;
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* dequeue_dl_entity();
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* start_dl_timer();
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* // [E]
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*
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* // server replenished
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* [6] E->D
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* dl_server_timer()
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* enqueue_dl_entity(REPLENISH)
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* replenish_dl_entity()
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* fwd-period
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* if (dl_throttled)
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* dl_throttled = 0;
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* __enqueue_dl_entity();
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* // [D]
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*
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* // deplete server runtime from idle
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* [7] B->C, C->C
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* dl_server_update_idle()
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* update_curr_dl_se() // idle = true
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* if (dl_defer && dl_throttled && dl_runtime_exceeded())
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* if (dl_defer_idle)
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* return;
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* dl_defer_running = 0;
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* hrtimer_try_to_cancel();
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* replenish_dl_new_period()
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* // fwd period
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* dl_throttled = 1;
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* dl_defer_armed = 1;
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* dl_defer_idle = 1;
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* start_dl_timer(); // restart timer
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* // [C]
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*
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* // stop idle server
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* [8] C->A
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* dl_server_timer()
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* if (dl_defer_idle)
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* dl_server_stop();
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* // [A]
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*
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*
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* digraph dl_server {
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* "A:init" -> "B:zero_laxity-wait" [label="1:dl_server_start"]
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* "A:init" -> "D:running" [label="1:dl_server_start"]
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* "B:zero_laxity-wait" -> "B:zero_laxity-wait" [label="2:dl_server_update"]
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* "B:zero_laxity-wait" -> "C:idle-wait" [label="7:dl_server_update_idle"]
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* "B:zero_laxity-wait" -> "D:running" [label="3:dl_server_timer"]
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* "C:idle-wait" -> "A:init" [label="8:dl_server_timer"]
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* "C:idle-wait" -> "B:zero_laxity-wait" [label="2:dl_server_update"]
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* "C:idle-wait" -> "C:idle-wait" [label="7:dl_server_update_idle"]
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* "D:running" -> "A:init" [label="4:pick_task_dl"]
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* "D:running" -> "E:replenish-wait" [label="5:update_curr_dl_se"]
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* "E:replenish-wait" -> "B:zero_laxity-wait" [label="2:dl_server_update"]
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* "E:replenish-wait" -> "D:running" [label="6:dl_server_timer"]
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* }
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*
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*
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* Notes:
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*
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* - When there are fair tasks running the most likely loop is [2]->[2].
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* the dl_server never actually runs, the timer never fires.
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*
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* - When there is actual fair starvation; the timer fires and starts the
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* dl_server. This will then throttle and replenish like a normal DL
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* task. Notably it will not 'defer' again.
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*
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* - When idle it will push the actication forward once, and then wait
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* for the timer to hit or a non-idle update to restart things.
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*/
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void dl_server_start(struct sched_dl_entity *dl_se)
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{
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struct rq *rq = dl_se->rq;
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