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1/*
2 * SPDX-License-Identifier: MIT
3 *
4 * Copyright © 2018 Intel Corporation
5 */
6
7#include <linux/mutex.h>
8
9#include "i915_drv.h"
10#include "i915_globals.h"
11#include "i915_request.h"
12#include "i915_scheduler.h"
13
14static struct i915_global_scheduler {
15 struct i915_global base;
16 struct kmem_cache *slab_dependencies;
17 struct kmem_cache *slab_priorities;
18} global;
19
20static DEFINE_SPINLOCK(schedule_lock);
21
22static const struct i915_request *
23node_to_request(const struct i915_sched_node *node)
24{
25 return container_of(node, const struct i915_request, sched);
26}
27
28static inline bool node_started(const struct i915_sched_node *node)
29{
30 return i915_request_started(node_to_request(node));
31}
32
33static inline bool node_signaled(const struct i915_sched_node *node)
34{
35 return i915_request_completed(node_to_request(node));
36}
37
38static inline struct i915_priolist *to_priolist(struct rb_node *rb)
39{
40 return rb_entry(rb, struct i915_priolist, node);
41}
42
43static void assert_priolists(struct intel_engine_execlists * const execlists)
44{
45 struct rb_node *rb;
46 long last_prio;
47
48 if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
49 return;
50
51 GEM_BUG_ON(rb_first_cached(&execlists->queue) !=
52 rb_first(&execlists->queue.rb_root));
53
54 last_prio = INT_MAX;
55 for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
56 const struct i915_priolist *p = to_priolist(rb);
57
58 GEM_BUG_ON(p->priority > last_prio);
59 last_prio = p->priority;
60 }
61}
62
63struct list_head *
64i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
65{
66 struct intel_engine_execlists * const execlists = &engine->execlists;
67 struct i915_priolist *p;
68 struct rb_node **parent, *rb;
69 bool first = true;
70
71 lockdep_assert_held(&engine->active.lock);
72 assert_priolists(execlists);
73
74 if (unlikely(execlists->no_priolist))
75 prio = I915_PRIORITY_NORMAL;
76
77find_priolist:
78 /* most positive priority is scheduled first, equal priorities fifo */
79 rb = NULL;
80 parent = &execlists->queue.rb_root.rb_node;
81 while (*parent) {
82 rb = *parent;
83 p = to_priolist(rb);
84 if (prio > p->priority) {
85 parent = &rb->rb_left;
86 } else if (prio < p->priority) {
87 parent = &rb->rb_right;
88 first = false;
89 } else {
90 return &p->requests;
91 }
92 }
93
94 if (prio == I915_PRIORITY_NORMAL) {
95 p = &execlists->default_priolist;
96 } else {
97 p = kmem_cache_alloc(global.slab_priorities, GFP_ATOMIC);
98 /* Convert an allocation failure to a priority bump */
99 if (unlikely(!p)) {
100 prio = I915_PRIORITY_NORMAL; /* recurses just once */
101
102 /* To maintain ordering with all rendering, after an
103 * allocation failure we have to disable all scheduling.
104 * Requests will then be executed in fifo, and schedule
105 * will ensure that dependencies are emitted in fifo.
106 * There will be still some reordering with existing
107 * requests, so if userspace lied about their
108 * dependencies that reordering may be visible.
109 */
110 execlists->no_priolist = true;
111 goto find_priolist;
112 }
113 }
114
115 p->priority = prio;
116 INIT_LIST_HEAD(&p->requests);
117
118 rb_link_node(&p->node, rb, parent);
119 rb_insert_color_cached(&p->node, &execlists->queue, first);
120
121 return &p->requests;
122}
123
124void __i915_priolist_free(struct i915_priolist *p)
125{
126 kmem_cache_free(global.slab_priorities, p);
127}
128
129struct sched_cache {
130 struct list_head *priolist;
131};
132
133static struct intel_engine_cs *
134sched_lock_engine(const struct i915_sched_node *node,
135 struct intel_engine_cs *locked,
136 struct sched_cache *cache)
137{
138 const struct i915_request *rq = node_to_request(node);
139 struct intel_engine_cs *engine;
140
141 GEM_BUG_ON(!locked);
142
143 /*
144 * Virtual engines complicate acquiring the engine timeline lock,
145 * as their rq->engine pointer is not stable until under that
146 * engine lock. The simple ploy we use is to take the lock then
147 * check that the rq still belongs to the newly locked engine.
148 */
149 while (locked != (engine = READ_ONCE(rq->engine))) {
150 spin_unlock(&locked->active.lock);
151 memset(cache, 0, sizeof(*cache));
152 spin_lock(&engine->active.lock);
153 locked = engine;
154 }
155
156 GEM_BUG_ON(locked != engine);
157 return locked;
158}
159
160static inline int rq_prio(const struct i915_request *rq)
161{
162 return rq->sched.attr.priority;
163}
164
165static inline bool need_preempt(int prio, int active)
166{
167 /*
168 * Allow preemption of low -> normal -> high, but we do
169 * not allow low priority tasks to preempt other low priority
170 * tasks under the impression that latency for low priority
171 * tasks does not matter (as much as background throughput),
172 * so kiss.
173 */
174 return prio >= max(I915_PRIORITY_NORMAL, active);
175}
176
177static void kick_submission(struct intel_engine_cs *engine,
178 const struct i915_request *rq,
179 int prio)
180{
181 const struct i915_request *inflight;
182
183 /*
184 * We only need to kick the tasklet once for the high priority
185 * new context we add into the queue.
186 */
187 if (prio <= engine->execlists.queue_priority_hint)
188 return;
189
190 rcu_read_lock();
191
192 /* Nothing currently active? We're overdue for a submission! */
193 inflight = execlists_active(&engine->execlists);
194 if (!inflight)
195 goto unlock;
196
197 /*
198 * If we are already the currently executing context, don't
199 * bother evaluating if we should preempt ourselves.
200 */
201 if (inflight->context == rq->context)
202 goto unlock;
203
204 ENGINE_TRACE(engine,
205 "bumping queue-priority-hint:%d for rq:%llx:%lld, inflight:%llx:%lld prio %d\n",
206 prio,
207 rq->fence.context, rq->fence.seqno,
208 inflight->fence.context, inflight->fence.seqno,
209 inflight->sched.attr.priority);
210
211 engine->execlists.queue_priority_hint = prio;
212 if (need_preempt(prio, rq_prio(inflight)))
213 tasklet_hi_schedule(&engine->execlists.tasklet);
214
215unlock:
216 rcu_read_unlock();
217}
218
219static void __i915_schedule(struct i915_sched_node *node,
220 const struct i915_sched_attr *attr)
221{
222 const int prio = max(attr->priority, node->attr.priority);
223 struct intel_engine_cs *engine;
224 struct i915_dependency *dep, *p;
225 struct i915_dependency stack;
226 struct sched_cache cache;
227 LIST_HEAD(dfs);
228
229 /* Needed in order to use the temporary link inside i915_dependency */
230 lockdep_assert_held(&schedule_lock);
231 GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
232
233 if (node_signaled(node))
234 return;
235
236 stack.signaler = node;
237 list_add(&stack.dfs_link, &dfs);
238
239 /*
240 * Recursively bump all dependent priorities to match the new request.
241 *
242 * A naive approach would be to use recursion:
243 * static void update_priorities(struct i915_sched_node *node, prio) {
244 * list_for_each_entry(dep, &node->signalers_list, signal_link)
245 * update_priorities(dep->signal, prio)
246 * queue_request(node);
247 * }
248 * but that may have unlimited recursion depth and so runs a very
249 * real risk of overunning the kernel stack. Instead, we build
250 * a flat list of all dependencies starting with the current request.
251 * As we walk the list of dependencies, we add all of its dependencies
252 * to the end of the list (this may include an already visited
253 * request) and continue to walk onwards onto the new dependencies. The
254 * end result is a topological list of requests in reverse order, the
255 * last element in the list is the request we must execute first.
256 */
257 list_for_each_entry(dep, &dfs, dfs_link) {
258 struct i915_sched_node *node = dep->signaler;
259
260 /* If we are already flying, we know we have no signalers */
261 if (node_started(node))
262 continue;
263
264 /*
265 * Within an engine, there can be no cycle, but we may
266 * refer to the same dependency chain multiple times
267 * (redundant dependencies are not eliminated) and across
268 * engines.
269 */
270 list_for_each_entry(p, &node->signalers_list, signal_link) {
271 GEM_BUG_ON(p == dep); /* no cycles! */
272
273 if (node_signaled(p->signaler))
274 continue;
275
276 if (prio > READ_ONCE(p->signaler->attr.priority))
277 list_move_tail(&p->dfs_link, &dfs);
278 }
279 }
280
281 /*
282 * If we didn't need to bump any existing priorities, and we haven't
283 * yet submitted this request (i.e. there is no potential race with
284 * execlists_submit_request()), we can set our own priority and skip
285 * acquiring the engine locks.
286 */
287 if (node->attr.priority == I915_PRIORITY_INVALID) {
288 GEM_BUG_ON(!list_empty(&node->link));
289 node->attr = *attr;
290
291 if (stack.dfs_link.next == stack.dfs_link.prev)
292 return;
293
294 __list_del_entry(&stack.dfs_link);
295 }
296
297 memset(&cache, 0, sizeof(cache));
298 engine = node_to_request(node)->engine;
299 spin_lock(&engine->active.lock);
300
301 /* Fifo and depth-first replacement ensure our deps execute before us */
302 engine = sched_lock_engine(node, engine, &cache);
303 list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
304 INIT_LIST_HEAD(&dep->dfs_link);
305
306 node = dep->signaler;
307 engine = sched_lock_engine(node, engine, &cache);
308 lockdep_assert_held(&engine->active.lock);
309
310 /* Recheck after acquiring the engine->timeline.lock */
311 if (prio <= node->attr.priority || node_signaled(node))
312 continue;
313
314 GEM_BUG_ON(node_to_request(node)->engine != engine);
315
316 WRITE_ONCE(node->attr.priority, prio);
317
318 /*
319 * Once the request is ready, it will be placed into the
320 * priority lists and then onto the HW runlist. Before the
321 * request is ready, it does not contribute to our preemption
322 * decisions and we can safely ignore it, as it will, and
323 * any preemption required, be dealt with upon submission.
324 * See engine->submit_request()
325 */
326 if (list_empty(&node->link))
327 continue;
328
329 if (i915_request_in_priority_queue(node_to_request(node))) {
330 if (!cache.priolist)
331 cache.priolist =
332 i915_sched_lookup_priolist(engine,
333 prio);
334 list_move_tail(&node->link, cache.priolist);
335 }
336
337 /* Defer (tasklet) submission until after all of our updates. */
338 kick_submission(engine, node_to_request(node), prio);
339 }
340
341 spin_unlock(&engine->active.lock);
342}
343
344void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
345{
346 spin_lock_irq(&schedule_lock);
347 __i915_schedule(&rq->sched, attr);
348 spin_unlock_irq(&schedule_lock);
349}
350
351void i915_sched_node_init(struct i915_sched_node *node)
352{
353 INIT_LIST_HEAD(&node->signalers_list);
354 INIT_LIST_HEAD(&node->waiters_list);
355 INIT_LIST_HEAD(&node->link);
356
357 i915_sched_node_reinit(node);
358}
359
360void i915_sched_node_reinit(struct i915_sched_node *node)
361{
362 node->attr.priority = I915_PRIORITY_INVALID;
363 node->semaphores = 0;
364 node->flags = 0;
365
366 GEM_BUG_ON(!list_empty(&node->signalers_list));
367 GEM_BUG_ON(!list_empty(&node->waiters_list));
368 GEM_BUG_ON(!list_empty(&node->link));
369}
370
371static struct i915_dependency *
372i915_dependency_alloc(void)
373{
374 return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
375}
376
377static void
378i915_dependency_free(struct i915_dependency *dep)
379{
380 kmem_cache_free(global.slab_dependencies, dep);
381}
382
383bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
384 struct i915_sched_node *signal,
385 struct i915_dependency *dep,
386 unsigned long flags)
387{
388 bool ret = false;
389
390 spin_lock_irq(&schedule_lock);
391
392 if (!node_signaled(signal)) {
393 INIT_LIST_HEAD(&dep->dfs_link);
394 dep->signaler = signal;
395 dep->waiter = node;
396 dep->flags = flags;
397
398 /* All set, now publish. Beware the lockless walkers. */
399 list_add_rcu(&dep->signal_link, &node->signalers_list);
400 list_add_rcu(&dep->wait_link, &signal->waiters_list);
401
402 /* Propagate the chains */
403 node->flags |= signal->flags;
404 ret = true;
405 }
406
407 spin_unlock_irq(&schedule_lock);
408
409 return ret;
410}
411
412int i915_sched_node_add_dependency(struct i915_sched_node *node,
413 struct i915_sched_node *signal,
414 unsigned long flags)
415{
416 struct i915_dependency *dep;
417
418 dep = i915_dependency_alloc();
419 if (!dep)
420 return -ENOMEM;
421
422 if (!__i915_sched_node_add_dependency(node, signal, dep,
423 flags | I915_DEPENDENCY_ALLOC))
424 i915_dependency_free(dep);
425
426 return 0;
427}
428
429void i915_sched_node_fini(struct i915_sched_node *node)
430{
431 struct i915_dependency *dep, *tmp;
432
433 spin_lock_irq(&schedule_lock);
434
435 /*
436 * Everyone we depended upon (the fences we wait to be signaled)
437 * should retire before us and remove themselves from our list.
438 * However, retirement is run independently on each timeline and
439 * so we may be called out-of-order.
440 */
441 list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
442 GEM_BUG_ON(!list_empty(&dep->dfs_link));
443
444 list_del_rcu(&dep->wait_link);
445 if (dep->flags & I915_DEPENDENCY_ALLOC)
446 i915_dependency_free(dep);
447 }
448 INIT_LIST_HEAD(&node->signalers_list);
449
450 /* Remove ourselves from everyone who depends upon us */
451 list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
452 GEM_BUG_ON(dep->signaler != node);
453 GEM_BUG_ON(!list_empty(&dep->dfs_link));
454
455 list_del_rcu(&dep->signal_link);
456 if (dep->flags & I915_DEPENDENCY_ALLOC)
457 i915_dependency_free(dep);
458 }
459 INIT_LIST_HEAD(&node->waiters_list);
460
461 spin_unlock_irq(&schedule_lock);
462}
463
464void i915_request_show_with_schedule(struct drm_printer *m,
465 const struct i915_request *rq,
466 const char *prefix,
467 int indent)
468{
469 struct i915_dependency *dep;
470
471 i915_request_show(m, rq, prefix, indent);
472 if (i915_request_completed(rq))
473 return;
474
475 rcu_read_lock();
476 for_each_signaler(dep, rq) {
477 const struct i915_request *signaler =
478 node_to_request(dep->signaler);
479
480 /* Dependencies along the same timeline are expected. */
481 if (signaler->timeline == rq->timeline)
482 continue;
483
484 if (__i915_request_is_complete(signaler))
485 continue;
486
487 i915_request_show(m, signaler, prefix, indent + 2);
488 }
489 rcu_read_unlock();
490}
491
492static void i915_global_scheduler_shrink(void)
493{
494 kmem_cache_shrink(global.slab_dependencies);
495 kmem_cache_shrink(global.slab_priorities);
496}
497
498static void i915_global_scheduler_exit(void)
499{
500 kmem_cache_destroy(global.slab_dependencies);
501 kmem_cache_destroy(global.slab_priorities);
502}
503
504static struct i915_global_scheduler global = { {
505 .shrink = i915_global_scheduler_shrink,
506 .exit = i915_global_scheduler_exit,
507} };
508
509int __init i915_global_scheduler_init(void)
510{
511 global.slab_dependencies = KMEM_CACHE(i915_dependency,
512 SLAB_HWCACHE_ALIGN |
513 SLAB_TYPESAFE_BY_RCU);
514 if (!global.slab_dependencies)
515 return -ENOMEM;
516
517 global.slab_priorities = KMEM_CACHE(i915_priolist, 0);
518 if (!global.slab_priorities)
519 goto err_priorities;
520
521 i915_global_register(&global.base);
522 return 0;
523
524err_priorities:
525 kmem_cache_destroy(global.slab_priorities);
526 return -ENOMEM;
527}
1/*
2 * SPDX-License-Identifier: MIT
3 *
4 * Copyright © 2018 Intel Corporation
5 */
6
7#include <linux/mutex.h>
8
9#include "i915_drv.h"
10#include "i915_globals.h"
11#include "i915_request.h"
12#include "i915_scheduler.h"
13
14static struct i915_global_scheduler {
15 struct i915_global base;
16 struct kmem_cache *slab_dependencies;
17 struct kmem_cache *slab_priorities;
18} global;
19
20static DEFINE_SPINLOCK(schedule_lock);
21
22static const struct i915_request *
23node_to_request(const struct i915_sched_node *node)
24{
25 return container_of(node, const struct i915_request, sched);
26}
27
28static inline bool node_started(const struct i915_sched_node *node)
29{
30 return i915_request_started(node_to_request(node));
31}
32
33static inline bool node_signaled(const struct i915_sched_node *node)
34{
35 return i915_request_completed(node_to_request(node));
36}
37
38static inline struct i915_priolist *to_priolist(struct rb_node *rb)
39{
40 return rb_entry(rb, struct i915_priolist, node);
41}
42
43static void assert_priolists(struct intel_engine_execlists * const execlists)
44{
45 struct rb_node *rb;
46 long last_prio, i;
47
48 if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
49 return;
50
51 GEM_BUG_ON(rb_first_cached(&execlists->queue) !=
52 rb_first(&execlists->queue.rb_root));
53
54 last_prio = (INT_MAX >> I915_USER_PRIORITY_SHIFT) + 1;
55 for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
56 const struct i915_priolist *p = to_priolist(rb);
57
58 GEM_BUG_ON(p->priority >= last_prio);
59 last_prio = p->priority;
60
61 GEM_BUG_ON(!p->used);
62 for (i = 0; i < ARRAY_SIZE(p->requests); i++) {
63 if (list_empty(&p->requests[i]))
64 continue;
65
66 GEM_BUG_ON(!(p->used & BIT(i)));
67 }
68 }
69}
70
71struct list_head *
72i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
73{
74 struct intel_engine_execlists * const execlists = &engine->execlists;
75 struct i915_priolist *p;
76 struct rb_node **parent, *rb;
77 bool first = true;
78 int idx, i;
79
80 lockdep_assert_held(&engine->active.lock);
81 assert_priolists(execlists);
82
83 /* buckets sorted from highest [in slot 0] to lowest priority */
84 idx = I915_PRIORITY_COUNT - (prio & I915_PRIORITY_MASK) - 1;
85 prio >>= I915_USER_PRIORITY_SHIFT;
86 if (unlikely(execlists->no_priolist))
87 prio = I915_PRIORITY_NORMAL;
88
89find_priolist:
90 /* most positive priority is scheduled first, equal priorities fifo */
91 rb = NULL;
92 parent = &execlists->queue.rb_root.rb_node;
93 while (*parent) {
94 rb = *parent;
95 p = to_priolist(rb);
96 if (prio > p->priority) {
97 parent = &rb->rb_left;
98 } else if (prio < p->priority) {
99 parent = &rb->rb_right;
100 first = false;
101 } else {
102 goto out;
103 }
104 }
105
106 if (prio == I915_PRIORITY_NORMAL) {
107 p = &execlists->default_priolist;
108 } else {
109 p = kmem_cache_alloc(global.slab_priorities, GFP_ATOMIC);
110 /* Convert an allocation failure to a priority bump */
111 if (unlikely(!p)) {
112 prio = I915_PRIORITY_NORMAL; /* recurses just once */
113
114 /* To maintain ordering with all rendering, after an
115 * allocation failure we have to disable all scheduling.
116 * Requests will then be executed in fifo, and schedule
117 * will ensure that dependencies are emitted in fifo.
118 * There will be still some reordering with existing
119 * requests, so if userspace lied about their
120 * dependencies that reordering may be visible.
121 */
122 execlists->no_priolist = true;
123 goto find_priolist;
124 }
125 }
126
127 p->priority = prio;
128 for (i = 0; i < ARRAY_SIZE(p->requests); i++)
129 INIT_LIST_HEAD(&p->requests[i]);
130 rb_link_node(&p->node, rb, parent);
131 rb_insert_color_cached(&p->node, &execlists->queue, first);
132 p->used = 0;
133
134out:
135 p->used |= BIT(idx);
136 return &p->requests[idx];
137}
138
139void __i915_priolist_free(struct i915_priolist *p)
140{
141 kmem_cache_free(global.slab_priorities, p);
142}
143
144struct sched_cache {
145 struct list_head *priolist;
146};
147
148static struct intel_engine_cs *
149sched_lock_engine(const struct i915_sched_node *node,
150 struct intel_engine_cs *locked,
151 struct sched_cache *cache)
152{
153 const struct i915_request *rq = node_to_request(node);
154 struct intel_engine_cs *engine;
155
156 GEM_BUG_ON(!locked);
157
158 /*
159 * Virtual engines complicate acquiring the engine timeline lock,
160 * as their rq->engine pointer is not stable until under that
161 * engine lock. The simple ploy we use is to take the lock then
162 * check that the rq still belongs to the newly locked engine.
163 */
164 while (locked != (engine = READ_ONCE(rq->engine))) {
165 spin_unlock(&locked->active.lock);
166 memset(cache, 0, sizeof(*cache));
167 spin_lock(&engine->active.lock);
168 locked = engine;
169 }
170
171 GEM_BUG_ON(locked != engine);
172 return locked;
173}
174
175static inline int rq_prio(const struct i915_request *rq)
176{
177 return rq->sched.attr.priority | __NO_PREEMPTION;
178}
179
180static inline bool need_preempt(int prio, int active)
181{
182 /*
183 * Allow preemption of low -> normal -> high, but we do
184 * not allow low priority tasks to preempt other low priority
185 * tasks under the impression that latency for low priority
186 * tasks does not matter (as much as background throughput),
187 * so kiss.
188 */
189 return prio >= max(I915_PRIORITY_NORMAL, active);
190}
191
192static void kick_submission(struct intel_engine_cs *engine,
193 const struct i915_request *rq,
194 int prio)
195{
196 const struct i915_request *inflight;
197
198 /*
199 * We only need to kick the tasklet once for the high priority
200 * new context we add into the queue.
201 */
202 if (prio <= engine->execlists.queue_priority_hint)
203 return;
204
205 rcu_read_lock();
206
207 /* Nothing currently active? We're overdue for a submission! */
208 inflight = execlists_active(&engine->execlists);
209 if (!inflight)
210 goto unlock;
211
212 /*
213 * If we are already the currently executing context, don't
214 * bother evaluating if we should preempt ourselves, or if
215 * we expect nothing to change as a result of running the
216 * tasklet, i.e. we have not change the priority queue
217 * sufficiently to oust the running context.
218 */
219 if (inflight->hw_context == rq->hw_context)
220 goto unlock;
221
222 engine->execlists.queue_priority_hint = prio;
223 if (need_preempt(prio, rq_prio(inflight)))
224 tasklet_hi_schedule(&engine->execlists.tasklet);
225
226unlock:
227 rcu_read_unlock();
228}
229
230static void __i915_schedule(struct i915_sched_node *node,
231 const struct i915_sched_attr *attr)
232{
233 struct intel_engine_cs *engine;
234 struct i915_dependency *dep, *p;
235 struct i915_dependency stack;
236 const int prio = attr->priority;
237 struct sched_cache cache;
238 LIST_HEAD(dfs);
239
240 /* Needed in order to use the temporary link inside i915_dependency */
241 lockdep_assert_held(&schedule_lock);
242 GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
243
244 if (prio <= READ_ONCE(node->attr.priority))
245 return;
246
247 if (node_signaled(node))
248 return;
249
250 stack.signaler = node;
251 list_add(&stack.dfs_link, &dfs);
252
253 /*
254 * Recursively bump all dependent priorities to match the new request.
255 *
256 * A naive approach would be to use recursion:
257 * static void update_priorities(struct i915_sched_node *node, prio) {
258 * list_for_each_entry(dep, &node->signalers_list, signal_link)
259 * update_priorities(dep->signal, prio)
260 * queue_request(node);
261 * }
262 * but that may have unlimited recursion depth and so runs a very
263 * real risk of overunning the kernel stack. Instead, we build
264 * a flat list of all dependencies starting with the current request.
265 * As we walk the list of dependencies, we add all of its dependencies
266 * to the end of the list (this may include an already visited
267 * request) and continue to walk onwards onto the new dependencies. The
268 * end result is a topological list of requests in reverse order, the
269 * last element in the list is the request we must execute first.
270 */
271 list_for_each_entry(dep, &dfs, dfs_link) {
272 struct i915_sched_node *node = dep->signaler;
273
274 /* If we are already flying, we know we have no signalers */
275 if (node_started(node))
276 continue;
277
278 /*
279 * Within an engine, there can be no cycle, but we may
280 * refer to the same dependency chain multiple times
281 * (redundant dependencies are not eliminated) and across
282 * engines.
283 */
284 list_for_each_entry(p, &node->signalers_list, signal_link) {
285 GEM_BUG_ON(p == dep); /* no cycles! */
286
287 if (node_signaled(p->signaler))
288 continue;
289
290 if (prio > READ_ONCE(p->signaler->attr.priority))
291 list_move_tail(&p->dfs_link, &dfs);
292 }
293 }
294
295 /*
296 * If we didn't need to bump any existing priorities, and we haven't
297 * yet submitted this request (i.e. there is no potential race with
298 * execlists_submit_request()), we can set our own priority and skip
299 * acquiring the engine locks.
300 */
301 if (node->attr.priority == I915_PRIORITY_INVALID) {
302 GEM_BUG_ON(!list_empty(&node->link));
303 node->attr = *attr;
304
305 if (stack.dfs_link.next == stack.dfs_link.prev)
306 return;
307
308 __list_del_entry(&stack.dfs_link);
309 }
310
311 memset(&cache, 0, sizeof(cache));
312 engine = node_to_request(node)->engine;
313 spin_lock(&engine->active.lock);
314
315 /* Fifo and depth-first replacement ensure our deps execute before us */
316 engine = sched_lock_engine(node, engine, &cache);
317 list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
318 INIT_LIST_HEAD(&dep->dfs_link);
319
320 node = dep->signaler;
321 engine = sched_lock_engine(node, engine, &cache);
322 lockdep_assert_held(&engine->active.lock);
323
324 /* Recheck after acquiring the engine->timeline.lock */
325 if (prio <= node->attr.priority || node_signaled(node))
326 continue;
327
328 GEM_BUG_ON(node_to_request(node)->engine != engine);
329
330 node->attr.priority = prio;
331
332 if (list_empty(&node->link)) {
333 /*
334 * If the request is not in the priolist queue because
335 * it is not yet runnable, then it doesn't contribute
336 * to our preemption decisions. On the other hand,
337 * if the request is on the HW, it too is not in the
338 * queue; but in that case we may still need to reorder
339 * the inflight requests.
340 */
341 continue;
342 }
343
344 if (!intel_engine_is_virtual(engine) &&
345 !i915_request_is_active(node_to_request(node))) {
346 if (!cache.priolist)
347 cache.priolist =
348 i915_sched_lookup_priolist(engine,
349 prio);
350 list_move_tail(&node->link, cache.priolist);
351 }
352
353 /* Defer (tasklet) submission until after all of our updates. */
354 kick_submission(engine, node_to_request(node), prio);
355 }
356
357 spin_unlock(&engine->active.lock);
358}
359
360void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
361{
362 spin_lock_irq(&schedule_lock);
363 __i915_schedule(&rq->sched, attr);
364 spin_unlock_irq(&schedule_lock);
365}
366
367static void __bump_priority(struct i915_sched_node *node, unsigned int bump)
368{
369 struct i915_sched_attr attr = node->attr;
370
371 attr.priority |= bump;
372 __i915_schedule(node, &attr);
373}
374
375void i915_schedule_bump_priority(struct i915_request *rq, unsigned int bump)
376{
377 unsigned long flags;
378
379 GEM_BUG_ON(bump & ~I915_PRIORITY_MASK);
380 if (READ_ONCE(rq->sched.attr.priority) & bump)
381 return;
382
383 spin_lock_irqsave(&schedule_lock, flags);
384 __bump_priority(&rq->sched, bump);
385 spin_unlock_irqrestore(&schedule_lock, flags);
386}
387
388void i915_sched_node_init(struct i915_sched_node *node)
389{
390 INIT_LIST_HEAD(&node->signalers_list);
391 INIT_LIST_HEAD(&node->waiters_list);
392 INIT_LIST_HEAD(&node->link);
393 node->attr.priority = I915_PRIORITY_INVALID;
394 node->semaphores = 0;
395 node->flags = 0;
396}
397
398static struct i915_dependency *
399i915_dependency_alloc(void)
400{
401 return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
402}
403
404static void
405i915_dependency_free(struct i915_dependency *dep)
406{
407 kmem_cache_free(global.slab_dependencies, dep);
408}
409
410bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
411 struct i915_sched_node *signal,
412 struct i915_dependency *dep,
413 unsigned long flags)
414{
415 bool ret = false;
416
417 spin_lock_irq(&schedule_lock);
418
419 if (!node_signaled(signal)) {
420 INIT_LIST_HEAD(&dep->dfs_link);
421 list_add(&dep->wait_link, &signal->waiters_list);
422 list_add(&dep->signal_link, &node->signalers_list);
423 dep->signaler = signal;
424 dep->waiter = node;
425 dep->flags = flags;
426
427 /* Keep track of whether anyone on this chain has a semaphore */
428 if (signal->flags & I915_SCHED_HAS_SEMAPHORE_CHAIN &&
429 !node_started(signal))
430 node->flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;
431
432 /*
433 * As we do not allow WAIT to preempt inflight requests,
434 * once we have executed a request, along with triggering
435 * any execution callbacks, we must preserve its ordering
436 * within the non-preemptible FIFO.
437 */
438 BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK);
439 if (flags & I915_DEPENDENCY_EXTERNAL)
440 __bump_priority(signal, __NO_PREEMPTION);
441
442 ret = true;
443 }
444
445 spin_unlock_irq(&schedule_lock);
446
447 return ret;
448}
449
450int i915_sched_node_add_dependency(struct i915_sched_node *node,
451 struct i915_sched_node *signal)
452{
453 struct i915_dependency *dep;
454
455 dep = i915_dependency_alloc();
456 if (!dep)
457 return -ENOMEM;
458
459 if (!__i915_sched_node_add_dependency(node, signal, dep,
460 I915_DEPENDENCY_EXTERNAL |
461 I915_DEPENDENCY_ALLOC))
462 i915_dependency_free(dep);
463
464 return 0;
465}
466
467void i915_sched_node_fini(struct i915_sched_node *node)
468{
469 struct i915_dependency *dep, *tmp;
470
471 spin_lock_irq(&schedule_lock);
472
473 /*
474 * Everyone we depended upon (the fences we wait to be signaled)
475 * should retire before us and remove themselves from our list.
476 * However, retirement is run independently on each timeline and
477 * so we may be called out-of-order.
478 */
479 list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
480 GEM_BUG_ON(!node_signaled(dep->signaler));
481 GEM_BUG_ON(!list_empty(&dep->dfs_link));
482
483 list_del(&dep->wait_link);
484 if (dep->flags & I915_DEPENDENCY_ALLOC)
485 i915_dependency_free(dep);
486 }
487
488 /* Remove ourselves from everyone who depends upon us */
489 list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
490 GEM_BUG_ON(dep->signaler != node);
491 GEM_BUG_ON(!list_empty(&dep->dfs_link));
492
493 list_del(&dep->signal_link);
494 if (dep->flags & I915_DEPENDENCY_ALLOC)
495 i915_dependency_free(dep);
496 }
497
498 spin_unlock_irq(&schedule_lock);
499}
500
501static void i915_global_scheduler_shrink(void)
502{
503 kmem_cache_shrink(global.slab_dependencies);
504 kmem_cache_shrink(global.slab_priorities);
505}
506
507static void i915_global_scheduler_exit(void)
508{
509 kmem_cache_destroy(global.slab_dependencies);
510 kmem_cache_destroy(global.slab_priorities);
511}
512
513static struct i915_global_scheduler global = { {
514 .shrink = i915_global_scheduler_shrink,
515 .exit = i915_global_scheduler_exit,
516} };
517
518int __init i915_global_scheduler_init(void)
519{
520 global.slab_dependencies = KMEM_CACHE(i915_dependency,
521 SLAB_HWCACHE_ALIGN);
522 if (!global.slab_dependencies)
523 return -ENOMEM;
524
525 global.slab_priorities = KMEM_CACHE(i915_priolist,
526 SLAB_HWCACHE_ALIGN);
527 if (!global.slab_priorities)
528 goto err_priorities;
529
530 i915_global_register(&global.base);
531 return 0;
532
533err_priorities:
534 kmem_cache_destroy(global.slab_priorities);
535 return -ENOMEM;
536}