1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | #include <linux/bug.h> |
3 | #include <linux/compiler.h> |
4 | #include <linux/export.h> |
5 | #include <linux/percpu.h> |
6 | #include <linux/processor.h> |
7 | #include <linux/smp.h> |
8 | #include <linux/topology.h> |
9 | #include <linux/sched/clock.h> |
10 | #include <asm/qspinlock.h> |
11 | #include <asm/paravirt.h> |
12 | |
13 | #define MAX_NODES 4 |
14 | |
15 | struct qnode { |
16 | struct qnode *next; |
17 | struct qspinlock *lock; |
18 | int cpu; |
19 | u8 sleepy; /* 1 if the previous vCPU was preempted or |
20 | * if the previous node was sleepy */ |
21 | u8 locked; /* 1 if lock acquired */ |
22 | }; |
23 | |
24 | struct qnodes { |
25 | int count; |
26 | struct qnode nodes[MAX_NODES]; |
27 | }; |
28 | |
29 | /* Tuning parameters */ |
30 | static int steal_spins __read_mostly = (1 << 5); |
31 | static int remote_steal_spins __read_mostly = (1 << 2); |
32 | #if _Q_SPIN_TRY_LOCK_STEAL == 1 |
33 | static const bool maybe_stealers = true; |
34 | #else |
35 | static bool maybe_stealers __read_mostly = true; |
36 | #endif |
37 | static int head_spins __read_mostly = (1 << 8); |
38 | |
39 | static bool pv_yield_owner __read_mostly = true; |
40 | static bool pv_yield_allow_steal __read_mostly = false; |
41 | static bool pv_spin_on_preempted_owner __read_mostly = false; |
42 | static bool pv_sleepy_lock __read_mostly = true; |
43 | static bool pv_sleepy_lock_sticky __read_mostly = false; |
44 | static u64 pv_sleepy_lock_interval_ns __read_mostly = 0; |
45 | static int pv_sleepy_lock_factor __read_mostly = 256; |
46 | static bool pv_yield_prev __read_mostly = true; |
47 | static bool pv_yield_sleepy_owner __read_mostly = true; |
48 | static bool pv_prod_head __read_mostly = false; |
49 | |
50 | static DEFINE_PER_CPU_ALIGNED(struct qnodes, qnodes); |
51 | static DEFINE_PER_CPU_ALIGNED(u64, sleepy_lock_seen_clock); |
52 | |
53 | #if _Q_SPIN_SPEC_BARRIER == 1 |
54 | #define spec_barrier() do { asm volatile("ori 31,31,0" ::: "memory"); } while (0) |
55 | #else |
56 | #define spec_barrier() do { } while (0) |
57 | #endif |
58 | |
59 | static __always_inline bool recently_sleepy(void) |
60 | { |
61 | /* pv_sleepy_lock is true when this is called */ |
62 | if (pv_sleepy_lock_interval_ns) { |
63 | u64 seen = this_cpu_read(sleepy_lock_seen_clock); |
64 | |
65 | if (seen) { |
66 | u64 delta = sched_clock() - seen; |
67 | if (delta < pv_sleepy_lock_interval_ns) |
68 | return true; |
69 | this_cpu_write(sleepy_lock_seen_clock, 0); |
70 | } |
71 | } |
72 | |
73 | return false; |
74 | } |
75 | |
76 | static __always_inline int get_steal_spins(bool paravirt, bool sleepy) |
77 | { |
78 | if (paravirt && sleepy) |
79 | return steal_spins * pv_sleepy_lock_factor; |
80 | else |
81 | return steal_spins; |
82 | } |
83 | |
84 | static __always_inline int get_remote_steal_spins(bool paravirt, bool sleepy) |
85 | { |
86 | if (paravirt && sleepy) |
87 | return remote_steal_spins * pv_sleepy_lock_factor; |
88 | else |
89 | return remote_steal_spins; |
90 | } |
91 | |
92 | static __always_inline int get_head_spins(bool paravirt, bool sleepy) |
93 | { |
94 | if (paravirt && sleepy) |
95 | return head_spins * pv_sleepy_lock_factor; |
96 | else |
97 | return head_spins; |
98 | } |
99 | |
100 | static inline u32 encode_tail_cpu(int cpu) |
101 | { |
102 | return (cpu + 1) << _Q_TAIL_CPU_OFFSET; |
103 | } |
104 | |
105 | static inline int decode_tail_cpu(u32 val) |
106 | { |
107 | return (val >> _Q_TAIL_CPU_OFFSET) - 1; |
108 | } |
109 | |
110 | static inline int get_owner_cpu(u32 val) |
111 | { |
112 | return (val & _Q_OWNER_CPU_MASK) >> _Q_OWNER_CPU_OFFSET; |
113 | } |
114 | |
115 | /* |
116 | * Try to acquire the lock if it was not already locked. If the tail matches |
117 | * mytail then clear it, otherwise leave it unchnaged. Return previous value. |
118 | * |
119 | * This is used by the head of the queue to acquire the lock and clean up |
120 | * its tail if it was the last one queued. |
121 | */ |
122 | static __always_inline u32 trylock_clean_tail(struct qspinlock *lock, u32 tail) |
123 | { |
124 | u32 newval = queued_spin_encode_locked_val(); |
125 | u32 prev, tmp; |
126 | |
127 | asm volatile( |
128 | "1: lwarx %0,0,%2,%7 # trylock_clean_tail \n" |
129 | /* This test is necessary if there could be stealers */ |
130 | " andi. %1,%0,%5 \n" |
131 | " bne 3f \n" |
132 | /* Test whether the lock tail == mytail */ |
133 | " and %1,%0,%6 \n" |
134 | " cmpw 0,%1,%3 \n" |
135 | /* Merge the new locked value */ |
136 | " or %1,%1,%4 \n" |
137 | " bne 2f \n" |
138 | /* If the lock tail matched, then clear it, otherwise leave it. */ |
139 | " andc %1,%1,%6 \n" |
140 | "2: stwcx. %1,0,%2 \n" |
141 | " bne- 1b \n" |
142 | "\t" PPC_ACQUIRE_BARRIER " \n" |
143 | "3: \n" |
144 | : "=&r" (prev), "=&r" (tmp) |
145 | : "r" (&lock->val), "r" (tail), "r" (newval), |
146 | "i" (_Q_LOCKED_VAL), |
147 | "r" (_Q_TAIL_CPU_MASK), |
148 | "i" (_Q_SPIN_EH_HINT) |
149 | : "cr0" , "memory" ); |
150 | |
151 | return prev; |
152 | } |
153 | |
154 | /* |
155 | * Publish our tail, replacing previous tail. Return previous value. |
156 | * |
157 | * This provides a release barrier for publishing node, this pairs with the |
158 | * acquire barrier in get_tail_qnode() when the next CPU finds this tail |
159 | * value. |
160 | */ |
161 | static __always_inline u32 publish_tail_cpu(struct qspinlock *lock, u32 tail) |
162 | { |
163 | u32 prev, tmp; |
164 | |
165 | kcsan_release(); |
166 | |
167 | asm volatile( |
168 | "\t" PPC_RELEASE_BARRIER " \n" |
169 | "1: lwarx %0,0,%2 # publish_tail_cpu \n" |
170 | " andc %1,%0,%4 \n" |
171 | " or %1,%1,%3 \n" |
172 | " stwcx. %1,0,%2 \n" |
173 | " bne- 1b \n" |
174 | : "=&r" (prev), "=&r" (tmp) |
175 | : "r" (&lock->val), "r" (tail), "r" (_Q_TAIL_CPU_MASK) |
176 | : "cr0" , "memory" ); |
177 | |
178 | return prev; |
179 | } |
180 | |
181 | static __always_inline u32 set_mustq(struct qspinlock *lock) |
182 | { |
183 | u32 prev; |
184 | |
185 | asm volatile( |
186 | "1: lwarx %0,0,%1 # set_mustq \n" |
187 | " or %0,%0,%2 \n" |
188 | " stwcx. %0,0,%1 \n" |
189 | " bne- 1b \n" |
190 | : "=&r" (prev) |
191 | : "r" (&lock->val), "r" (_Q_MUST_Q_VAL) |
192 | : "cr0" , "memory" ); |
193 | |
194 | return prev; |
195 | } |
196 | |
197 | static __always_inline u32 clear_mustq(struct qspinlock *lock) |
198 | { |
199 | u32 prev; |
200 | |
201 | asm volatile( |
202 | "1: lwarx %0,0,%1 # clear_mustq \n" |
203 | " andc %0,%0,%2 \n" |
204 | " stwcx. %0,0,%1 \n" |
205 | " bne- 1b \n" |
206 | : "=&r" (prev) |
207 | : "r" (&lock->val), "r" (_Q_MUST_Q_VAL) |
208 | : "cr0" , "memory" ); |
209 | |
210 | return prev; |
211 | } |
212 | |
213 | static __always_inline bool try_set_sleepy(struct qspinlock *lock, u32 old) |
214 | { |
215 | u32 prev; |
216 | u32 new = old | _Q_SLEEPY_VAL; |
217 | |
218 | BUG_ON(!(old & _Q_LOCKED_VAL)); |
219 | BUG_ON(old & _Q_SLEEPY_VAL); |
220 | |
221 | asm volatile( |
222 | "1: lwarx %0,0,%1 # try_set_sleepy \n" |
223 | " cmpw 0,%0,%2 \n" |
224 | " bne- 2f \n" |
225 | " stwcx. %3,0,%1 \n" |
226 | " bne- 1b \n" |
227 | "2: \n" |
228 | : "=&r" (prev) |
229 | : "r" (&lock->val), "r" (old), "r" (new) |
230 | : "cr0" , "memory" ); |
231 | |
232 | return likely(prev == old); |
233 | } |
234 | |
235 | static __always_inline void seen_sleepy_owner(struct qspinlock *lock, u32 val) |
236 | { |
237 | if (pv_sleepy_lock) { |
238 | if (pv_sleepy_lock_interval_ns) |
239 | this_cpu_write(sleepy_lock_seen_clock, sched_clock()); |
240 | if (!(val & _Q_SLEEPY_VAL)) |
241 | try_set_sleepy(lock, old: val); |
242 | } |
243 | } |
244 | |
245 | static __always_inline void seen_sleepy_lock(void) |
246 | { |
247 | if (pv_sleepy_lock && pv_sleepy_lock_interval_ns) |
248 | this_cpu_write(sleepy_lock_seen_clock, sched_clock()); |
249 | } |
250 | |
251 | static __always_inline void seen_sleepy_node(void) |
252 | { |
253 | if (pv_sleepy_lock) { |
254 | if (pv_sleepy_lock_interval_ns) |
255 | this_cpu_write(sleepy_lock_seen_clock, sched_clock()); |
256 | /* Don't set sleepy because we likely have a stale val */ |
257 | } |
258 | } |
259 | |
260 | static struct qnode *get_tail_qnode(struct qspinlock *lock, int prev_cpu) |
261 | { |
262 | struct qnodes *qnodesp = per_cpu_ptr(&qnodes, prev_cpu); |
263 | int idx; |
264 | |
265 | /* |
266 | * After publishing the new tail and finding a previous tail in the |
267 | * previous val (which is the control dependency), this barrier |
268 | * orders the release barrier in publish_tail_cpu performed by the |
269 | * last CPU, with subsequently looking at its qnode structures |
270 | * after the barrier. |
271 | */ |
272 | smp_acquire__after_ctrl_dep(); |
273 | |
274 | for (idx = 0; idx < MAX_NODES; idx++) { |
275 | struct qnode *qnode = &qnodesp->nodes[idx]; |
276 | if (qnode->lock == lock) |
277 | return qnode; |
278 | } |
279 | |
280 | BUG(); |
281 | } |
282 | |
283 | /* Called inside spin_begin(). Returns whether or not the vCPU was preempted. */ |
284 | static __always_inline bool __yield_to_locked_owner(struct qspinlock *lock, u32 val, bool paravirt, bool mustq) |
285 | { |
286 | int owner; |
287 | u32 yield_count; |
288 | bool preempted = false; |
289 | |
290 | BUG_ON(!(val & _Q_LOCKED_VAL)); |
291 | |
292 | if (!paravirt) |
293 | goto relax; |
294 | |
295 | if (!pv_yield_owner) |
296 | goto relax; |
297 | |
298 | owner = get_owner_cpu(val); |
299 | yield_count = yield_count_of(owner); |
300 | |
301 | if ((yield_count & 1) == 0) |
302 | goto relax; /* owner vcpu is running */ |
303 | |
304 | spin_end(); |
305 | |
306 | seen_sleepy_owner(lock, val); |
307 | preempted = true; |
308 | |
309 | /* |
310 | * Read the lock word after sampling the yield count. On the other side |
311 | * there may a wmb because the yield count update is done by the |
312 | * hypervisor preemption and the value update by the OS, however this |
313 | * ordering might reduce the chance of out of order accesses and |
314 | * improve the heuristic. |
315 | */ |
316 | smp_rmb(); |
317 | |
318 | if (READ_ONCE(lock->val) == val) { |
319 | if (mustq) |
320 | clear_mustq(lock); |
321 | yield_to_preempted(owner, yield_count); |
322 | if (mustq) |
323 | set_mustq(lock); |
324 | spin_begin(); |
325 | |
326 | /* Don't relax if we yielded. Maybe we should? */ |
327 | return preempted; |
328 | } |
329 | spin_begin(); |
330 | relax: |
331 | spin_cpu_relax(); |
332 | |
333 | return preempted; |
334 | } |
335 | |
336 | /* Called inside spin_begin(). Returns whether or not the vCPU was preempted. */ |
337 | static __always_inline bool yield_to_locked_owner(struct qspinlock *lock, u32 val, bool paravirt) |
338 | { |
339 | return __yield_to_locked_owner(lock, val, paravirt, mustq: false); |
340 | } |
341 | |
342 | /* Called inside spin_begin(). Returns whether or not the vCPU was preempted. */ |
343 | static __always_inline bool yield_head_to_locked_owner(struct qspinlock *lock, u32 val, bool paravirt) |
344 | { |
345 | bool mustq = false; |
346 | |
347 | if ((val & _Q_MUST_Q_VAL) && pv_yield_allow_steal) |
348 | mustq = true; |
349 | |
350 | return __yield_to_locked_owner(lock, val, paravirt, mustq); |
351 | } |
352 | |
353 | static __always_inline void propagate_sleepy(struct qnode *node, u32 val, bool paravirt) |
354 | { |
355 | struct qnode *next; |
356 | int owner; |
357 | |
358 | if (!paravirt) |
359 | return; |
360 | if (!pv_yield_sleepy_owner) |
361 | return; |
362 | |
363 | next = READ_ONCE(node->next); |
364 | if (!next) |
365 | return; |
366 | |
367 | if (next->sleepy) |
368 | return; |
369 | |
370 | owner = get_owner_cpu(val); |
371 | if (vcpu_is_preempted(cpu: owner)) |
372 | next->sleepy = 1; |
373 | } |
374 | |
375 | /* Called inside spin_begin() */ |
376 | static __always_inline bool yield_to_prev(struct qspinlock *lock, struct qnode *node, int prev_cpu, bool paravirt) |
377 | { |
378 | u32 yield_count; |
379 | bool preempted = false; |
380 | |
381 | if (!paravirt) |
382 | goto relax; |
383 | |
384 | if (!pv_yield_sleepy_owner) |
385 | goto yield_prev; |
386 | |
387 | /* |
388 | * If the previous waiter was preempted it might not be able to |
389 | * propagate sleepy to us, so check the lock in that case too. |
390 | */ |
391 | if (node->sleepy || vcpu_is_preempted(cpu: prev_cpu)) { |
392 | u32 val = READ_ONCE(lock->val); |
393 | |
394 | if (val & _Q_LOCKED_VAL) { |
395 | if (node->next && !node->next->sleepy) { |
396 | /* |
397 | * Propagate sleepy to next waiter. Only if |
398 | * owner is preempted, which allows the queue |
399 | * to become "non-sleepy" if vCPU preemption |
400 | * ceases to occur, even if the lock remains |
401 | * highly contended. |
402 | */ |
403 | if (vcpu_is_preempted(cpu: get_owner_cpu(val))) |
404 | node->next->sleepy = 1; |
405 | } |
406 | |
407 | preempted = yield_to_locked_owner(lock, val, paravirt); |
408 | if (preempted) |
409 | return preempted; |
410 | } |
411 | node->sleepy = false; |
412 | } |
413 | |
414 | yield_prev: |
415 | if (!pv_yield_prev) |
416 | goto relax; |
417 | |
418 | yield_count = yield_count_of(prev_cpu); |
419 | if ((yield_count & 1) == 0) |
420 | goto relax; /* owner vcpu is running */ |
421 | |
422 | spin_end(); |
423 | |
424 | preempted = true; |
425 | seen_sleepy_node(); |
426 | |
427 | smp_rmb(); /* See __yield_to_locked_owner comment */ |
428 | |
429 | if (!READ_ONCE(node->locked)) { |
430 | yield_to_preempted(prev_cpu, yield_count); |
431 | spin_begin(); |
432 | return preempted; |
433 | } |
434 | spin_begin(); |
435 | |
436 | relax: |
437 | spin_cpu_relax(); |
438 | |
439 | return preempted; |
440 | } |
441 | |
442 | static __always_inline bool steal_break(u32 val, int iters, bool paravirt, bool sleepy) |
443 | { |
444 | if (iters >= get_steal_spins(paravirt, sleepy)) |
445 | return true; |
446 | |
447 | if (IS_ENABLED(CONFIG_NUMA) && |
448 | (iters >= get_remote_steal_spins(paravirt, sleepy))) { |
449 | int cpu = get_owner_cpu(val); |
450 | if (numa_node_id() != cpu_to_node(cpu)) |
451 | return true; |
452 | } |
453 | return false; |
454 | } |
455 | |
456 | static __always_inline bool try_to_steal_lock(struct qspinlock *lock, bool paravirt) |
457 | { |
458 | bool seen_preempted = false; |
459 | bool sleepy = false; |
460 | int iters = 0; |
461 | u32 val; |
462 | |
463 | if (!steal_spins) { |
464 | /* XXX: should spin_on_preempted_owner do anything here? */ |
465 | return false; |
466 | } |
467 | |
468 | /* Attempt to steal the lock */ |
469 | spin_begin(); |
470 | do { |
471 | bool preempted = false; |
472 | |
473 | val = READ_ONCE(lock->val); |
474 | if (val & _Q_MUST_Q_VAL) |
475 | break; |
476 | spec_barrier(); |
477 | |
478 | if (unlikely(!(val & _Q_LOCKED_VAL))) { |
479 | spin_end(); |
480 | if (__queued_spin_trylock_steal(lock)) |
481 | return true; |
482 | spin_begin(); |
483 | } else { |
484 | preempted = yield_to_locked_owner(lock, val, paravirt); |
485 | } |
486 | |
487 | if (paravirt && pv_sleepy_lock) { |
488 | if (!sleepy) { |
489 | if (val & _Q_SLEEPY_VAL) { |
490 | seen_sleepy_lock(); |
491 | sleepy = true; |
492 | } else if (recently_sleepy()) { |
493 | sleepy = true; |
494 | } |
495 | } |
496 | if (pv_sleepy_lock_sticky && seen_preempted && |
497 | !(val & _Q_SLEEPY_VAL)) { |
498 | if (try_set_sleepy(lock, old: val)) |
499 | val |= _Q_SLEEPY_VAL; |
500 | } |
501 | } |
502 | |
503 | if (preempted) { |
504 | seen_preempted = true; |
505 | sleepy = true; |
506 | if (!pv_spin_on_preempted_owner) |
507 | iters++; |
508 | /* |
509 | * pv_spin_on_preempted_owner don't increase iters |
510 | * while the owner is preempted -- we won't interfere |
511 | * with it by definition. This could introduce some |
512 | * latency issue if we continually observe preempted |
513 | * owners, but hopefully that's a rare corner case of |
514 | * a badly oversubscribed system. |
515 | */ |
516 | } else { |
517 | iters++; |
518 | } |
519 | } while (!steal_break(val, iters, paravirt, sleepy)); |
520 | |
521 | spin_end(); |
522 | |
523 | return false; |
524 | } |
525 | |
526 | static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, bool paravirt) |
527 | { |
528 | struct qnodes *qnodesp; |
529 | struct qnode *next, *node; |
530 | u32 val, old, tail; |
531 | bool seen_preempted = false; |
532 | bool sleepy = false; |
533 | bool mustq = false; |
534 | int idx; |
535 | int iters = 0; |
536 | |
537 | BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS)); |
538 | |
539 | qnodesp = this_cpu_ptr(&qnodes); |
540 | if (unlikely(qnodesp->count >= MAX_NODES)) { |
541 | spec_barrier(); |
542 | while (!queued_spin_trylock(lock)) |
543 | cpu_relax(); |
544 | return; |
545 | } |
546 | |
547 | idx = qnodesp->count++; |
548 | /* |
549 | * Ensure that we increment the head node->count before initialising |
550 | * the actual node. If the compiler is kind enough to reorder these |
551 | * stores, then an IRQ could overwrite our assignments. |
552 | */ |
553 | barrier(); |
554 | node = &qnodesp->nodes[idx]; |
555 | node->next = NULL; |
556 | node->lock = lock; |
557 | node->cpu = smp_processor_id(); |
558 | node->sleepy = 0; |
559 | node->locked = 0; |
560 | |
561 | tail = encode_tail_cpu(cpu: node->cpu); |
562 | |
563 | /* |
564 | * Assign all attributes of a node before it can be published. |
565 | * Issues an lwsync, serving as a release barrier, as well as a |
566 | * compiler barrier. |
567 | */ |
568 | old = publish_tail_cpu(lock, tail); |
569 | |
570 | /* |
571 | * If there was a previous node; link it and wait until reaching the |
572 | * head of the waitqueue. |
573 | */ |
574 | if (old & _Q_TAIL_CPU_MASK) { |
575 | int prev_cpu = decode_tail_cpu(val: old); |
576 | struct qnode *prev = get_tail_qnode(lock, prev_cpu); |
577 | |
578 | /* Link @node into the waitqueue. */ |
579 | WRITE_ONCE(prev->next, node); |
580 | |
581 | /* Wait for mcs node lock to be released */ |
582 | spin_begin(); |
583 | while (!READ_ONCE(node->locked)) { |
584 | spec_barrier(); |
585 | |
586 | if (yield_to_prev(lock, node, prev_cpu, paravirt)) |
587 | seen_preempted = true; |
588 | } |
589 | spec_barrier(); |
590 | spin_end(); |
591 | |
592 | smp_rmb(); /* acquire barrier for the mcs lock */ |
593 | |
594 | /* |
595 | * Generic qspinlocks have this prefetch here, but it seems |
596 | * like it could cause additional line transitions because |
597 | * the waiter will keep loading from it. |
598 | */ |
599 | if (_Q_SPIN_PREFETCH_NEXT) { |
600 | next = READ_ONCE(node->next); |
601 | if (next) |
602 | prefetchw(x: next); |
603 | } |
604 | } |
605 | |
606 | /* We're at the head of the waitqueue, wait for the lock. */ |
607 | again: |
608 | spin_begin(); |
609 | for (;;) { |
610 | bool preempted; |
611 | |
612 | val = READ_ONCE(lock->val); |
613 | if (!(val & _Q_LOCKED_VAL)) |
614 | break; |
615 | spec_barrier(); |
616 | |
617 | if (paravirt && pv_sleepy_lock && maybe_stealers) { |
618 | if (!sleepy) { |
619 | if (val & _Q_SLEEPY_VAL) { |
620 | seen_sleepy_lock(); |
621 | sleepy = true; |
622 | } else if (recently_sleepy()) { |
623 | sleepy = true; |
624 | } |
625 | } |
626 | if (pv_sleepy_lock_sticky && seen_preempted && |
627 | !(val & _Q_SLEEPY_VAL)) { |
628 | if (try_set_sleepy(lock, old: val)) |
629 | val |= _Q_SLEEPY_VAL; |
630 | } |
631 | } |
632 | |
633 | propagate_sleepy(node, val, paravirt); |
634 | preempted = yield_head_to_locked_owner(lock, val, paravirt); |
635 | if (!maybe_stealers) |
636 | continue; |
637 | |
638 | if (preempted) |
639 | seen_preempted = true; |
640 | |
641 | if (paravirt && preempted) { |
642 | sleepy = true; |
643 | |
644 | if (!pv_spin_on_preempted_owner) |
645 | iters++; |
646 | } else { |
647 | iters++; |
648 | } |
649 | |
650 | if (!mustq && iters >= get_head_spins(paravirt, sleepy)) { |
651 | mustq = true; |
652 | set_mustq(lock); |
653 | val |= _Q_MUST_Q_VAL; |
654 | } |
655 | } |
656 | spec_barrier(); |
657 | spin_end(); |
658 | |
659 | /* If we're the last queued, must clean up the tail. */ |
660 | old = trylock_clean_tail(lock, tail); |
661 | if (unlikely(old & _Q_LOCKED_VAL)) { |
662 | BUG_ON(!maybe_stealers); |
663 | goto again; /* Can only be true if maybe_stealers. */ |
664 | } |
665 | |
666 | if ((old & _Q_TAIL_CPU_MASK) == tail) |
667 | goto release; /* We were the tail, no next. */ |
668 | |
669 | /* There is a next, must wait for node->next != NULL (MCS protocol) */ |
670 | next = READ_ONCE(node->next); |
671 | if (!next) { |
672 | spin_begin(); |
673 | while (!(next = READ_ONCE(node->next))) |
674 | cpu_relax(); |
675 | spin_end(); |
676 | } |
677 | spec_barrier(); |
678 | |
679 | /* |
680 | * Unlock the next mcs waiter node. Release barrier is not required |
681 | * here because the acquirer is only accessing the lock word, and |
682 | * the acquire barrier we took the lock with orders that update vs |
683 | * this store to locked. The corresponding barrier is the smp_rmb() |
684 | * acquire barrier for mcs lock, above. |
685 | */ |
686 | if (paravirt && pv_prod_head) { |
687 | int next_cpu = next->cpu; |
688 | WRITE_ONCE(next->locked, 1); |
689 | if (_Q_SPIN_MISO) |
690 | asm volatile("miso" ::: "memory" ); |
691 | if (vcpu_is_preempted(cpu: next_cpu)) |
692 | prod_cpu(next_cpu); |
693 | } else { |
694 | WRITE_ONCE(next->locked, 1); |
695 | if (_Q_SPIN_MISO) |
696 | asm volatile("miso" ::: "memory" ); |
697 | } |
698 | |
699 | release: |
700 | qnodesp->count--; /* release the node */ |
701 | } |
702 | |
703 | void queued_spin_lock_slowpath(struct qspinlock *lock) |
704 | { |
705 | /* |
706 | * This looks funny, but it induces the compiler to inline both |
707 | * sides of the branch rather than share code as when the condition |
708 | * is passed as the paravirt argument to the functions. |
709 | */ |
710 | if (IS_ENABLED(CONFIG_PARAVIRT_SPINLOCKS) && is_shared_processor()) { |
711 | if (try_to_steal_lock(lock, paravirt: true)) { |
712 | spec_barrier(); |
713 | return; |
714 | } |
715 | queued_spin_lock_mcs_queue(lock, paravirt: true); |
716 | } else { |
717 | if (try_to_steal_lock(lock, paravirt: false)) { |
718 | spec_barrier(); |
719 | return; |
720 | } |
721 | queued_spin_lock_mcs_queue(lock, paravirt: false); |
722 | } |
723 | } |
724 | EXPORT_SYMBOL(queued_spin_lock_slowpath); |
725 | |
726 | #ifdef CONFIG_PARAVIRT_SPINLOCKS |
727 | void pv_spinlocks_init(void) |
728 | { |
729 | } |
730 | #endif |
731 | |
732 | #include <linux/debugfs.h> |
733 | static int steal_spins_set(void *data, u64 val) |
734 | { |
735 | #if _Q_SPIN_TRY_LOCK_STEAL == 1 |
736 | /* MAYBE_STEAL remains true */ |
737 | steal_spins = val; |
738 | #else |
739 | static DEFINE_MUTEX(lock); |
740 | |
741 | /* |
742 | * The lock slow path has a !maybe_stealers case that can assume |
743 | * the head of queue will not see concurrent waiters. That waiter |
744 | * is unsafe in the presence of stealers, so must keep them away |
745 | * from one another. |
746 | */ |
747 | |
748 | mutex_lock(&lock); |
749 | if (val && !steal_spins) { |
750 | maybe_stealers = true; |
751 | /* wait for queue head waiter to go away */ |
752 | synchronize_rcu(); |
753 | steal_spins = val; |
754 | } else if (!val && steal_spins) { |
755 | steal_spins = val; |
756 | /* wait for all possible stealers to go away */ |
757 | synchronize_rcu(); |
758 | maybe_stealers = false; |
759 | } else { |
760 | steal_spins = val; |
761 | } |
762 | mutex_unlock(lock: &lock); |
763 | #endif |
764 | |
765 | return 0; |
766 | } |
767 | |
768 | static int steal_spins_get(void *data, u64 *val) |
769 | { |
770 | *val = steal_spins; |
771 | |
772 | return 0; |
773 | } |
774 | |
775 | DEFINE_SIMPLE_ATTRIBUTE(fops_steal_spins, steal_spins_get, steal_spins_set, "%llu\n" ); |
776 | |
777 | static int remote_steal_spins_set(void *data, u64 val) |
778 | { |
779 | remote_steal_spins = val; |
780 | |
781 | return 0; |
782 | } |
783 | |
784 | static int remote_steal_spins_get(void *data, u64 *val) |
785 | { |
786 | *val = remote_steal_spins; |
787 | |
788 | return 0; |
789 | } |
790 | |
791 | DEFINE_SIMPLE_ATTRIBUTE(fops_remote_steal_spins, remote_steal_spins_get, remote_steal_spins_set, "%llu\n" ); |
792 | |
793 | static int head_spins_set(void *data, u64 val) |
794 | { |
795 | head_spins = val; |
796 | |
797 | return 0; |
798 | } |
799 | |
800 | static int head_spins_get(void *data, u64 *val) |
801 | { |
802 | *val = head_spins; |
803 | |
804 | return 0; |
805 | } |
806 | |
807 | DEFINE_SIMPLE_ATTRIBUTE(fops_head_spins, head_spins_get, head_spins_set, "%llu\n" ); |
808 | |
809 | static int pv_yield_owner_set(void *data, u64 val) |
810 | { |
811 | pv_yield_owner = !!val; |
812 | |
813 | return 0; |
814 | } |
815 | |
816 | static int pv_yield_owner_get(void *data, u64 *val) |
817 | { |
818 | *val = pv_yield_owner; |
819 | |
820 | return 0; |
821 | } |
822 | |
823 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_yield_owner, pv_yield_owner_get, pv_yield_owner_set, "%llu\n" ); |
824 | |
825 | static int pv_yield_allow_steal_set(void *data, u64 val) |
826 | { |
827 | pv_yield_allow_steal = !!val; |
828 | |
829 | return 0; |
830 | } |
831 | |
832 | static int pv_yield_allow_steal_get(void *data, u64 *val) |
833 | { |
834 | *val = pv_yield_allow_steal; |
835 | |
836 | return 0; |
837 | } |
838 | |
839 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_yield_allow_steal, pv_yield_allow_steal_get, pv_yield_allow_steal_set, "%llu\n" ); |
840 | |
841 | static int pv_spin_on_preempted_owner_set(void *data, u64 val) |
842 | { |
843 | pv_spin_on_preempted_owner = !!val; |
844 | |
845 | return 0; |
846 | } |
847 | |
848 | static int pv_spin_on_preempted_owner_get(void *data, u64 *val) |
849 | { |
850 | *val = pv_spin_on_preempted_owner; |
851 | |
852 | return 0; |
853 | } |
854 | |
855 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_spin_on_preempted_owner, pv_spin_on_preempted_owner_get, pv_spin_on_preempted_owner_set, "%llu\n" ); |
856 | |
857 | static int pv_sleepy_lock_set(void *data, u64 val) |
858 | { |
859 | pv_sleepy_lock = !!val; |
860 | |
861 | return 0; |
862 | } |
863 | |
864 | static int pv_sleepy_lock_get(void *data, u64 *val) |
865 | { |
866 | *val = pv_sleepy_lock; |
867 | |
868 | return 0; |
869 | } |
870 | |
871 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_sleepy_lock, pv_sleepy_lock_get, pv_sleepy_lock_set, "%llu\n" ); |
872 | |
873 | static int pv_sleepy_lock_sticky_set(void *data, u64 val) |
874 | { |
875 | pv_sleepy_lock_sticky = !!val; |
876 | |
877 | return 0; |
878 | } |
879 | |
880 | static int pv_sleepy_lock_sticky_get(void *data, u64 *val) |
881 | { |
882 | *val = pv_sleepy_lock_sticky; |
883 | |
884 | return 0; |
885 | } |
886 | |
887 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_sleepy_lock_sticky, pv_sleepy_lock_sticky_get, pv_sleepy_lock_sticky_set, "%llu\n" ); |
888 | |
889 | static int pv_sleepy_lock_interval_ns_set(void *data, u64 val) |
890 | { |
891 | pv_sleepy_lock_interval_ns = val; |
892 | |
893 | return 0; |
894 | } |
895 | |
896 | static int pv_sleepy_lock_interval_ns_get(void *data, u64 *val) |
897 | { |
898 | *val = pv_sleepy_lock_interval_ns; |
899 | |
900 | return 0; |
901 | } |
902 | |
903 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_sleepy_lock_interval_ns, pv_sleepy_lock_interval_ns_get, pv_sleepy_lock_interval_ns_set, "%llu\n" ); |
904 | |
905 | static int pv_sleepy_lock_factor_set(void *data, u64 val) |
906 | { |
907 | pv_sleepy_lock_factor = val; |
908 | |
909 | return 0; |
910 | } |
911 | |
912 | static int pv_sleepy_lock_factor_get(void *data, u64 *val) |
913 | { |
914 | *val = pv_sleepy_lock_factor; |
915 | |
916 | return 0; |
917 | } |
918 | |
919 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_sleepy_lock_factor, pv_sleepy_lock_factor_get, pv_sleepy_lock_factor_set, "%llu\n" ); |
920 | |
921 | static int pv_yield_prev_set(void *data, u64 val) |
922 | { |
923 | pv_yield_prev = !!val; |
924 | |
925 | return 0; |
926 | } |
927 | |
928 | static int pv_yield_prev_get(void *data, u64 *val) |
929 | { |
930 | *val = pv_yield_prev; |
931 | |
932 | return 0; |
933 | } |
934 | |
935 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_yield_prev, pv_yield_prev_get, pv_yield_prev_set, "%llu\n" ); |
936 | |
937 | static int pv_yield_sleepy_owner_set(void *data, u64 val) |
938 | { |
939 | pv_yield_sleepy_owner = !!val; |
940 | |
941 | return 0; |
942 | } |
943 | |
944 | static int pv_yield_sleepy_owner_get(void *data, u64 *val) |
945 | { |
946 | *val = pv_yield_sleepy_owner; |
947 | |
948 | return 0; |
949 | } |
950 | |
951 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_yield_sleepy_owner, pv_yield_sleepy_owner_get, pv_yield_sleepy_owner_set, "%llu\n" ); |
952 | |
953 | static int pv_prod_head_set(void *data, u64 val) |
954 | { |
955 | pv_prod_head = !!val; |
956 | |
957 | return 0; |
958 | } |
959 | |
960 | static int pv_prod_head_get(void *data, u64 *val) |
961 | { |
962 | *val = pv_prod_head; |
963 | |
964 | return 0; |
965 | } |
966 | |
967 | DEFINE_SIMPLE_ATTRIBUTE(fops_pv_prod_head, pv_prod_head_get, pv_prod_head_set, "%llu\n" ); |
968 | |
969 | static __init int spinlock_debugfs_init(void) |
970 | { |
971 | debugfs_create_file(name: "qspl_steal_spins" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_steal_spins); |
972 | debugfs_create_file(name: "qspl_remote_steal_spins" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_remote_steal_spins); |
973 | debugfs_create_file(name: "qspl_head_spins" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_head_spins); |
974 | if (is_shared_processor()) { |
975 | debugfs_create_file(name: "qspl_pv_yield_owner" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_yield_owner); |
976 | debugfs_create_file(name: "qspl_pv_yield_allow_steal" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_yield_allow_steal); |
977 | debugfs_create_file(name: "qspl_pv_spin_on_preempted_owner" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_spin_on_preempted_owner); |
978 | debugfs_create_file(name: "qspl_pv_sleepy_lock" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_sleepy_lock); |
979 | debugfs_create_file(name: "qspl_pv_sleepy_lock_sticky" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_sleepy_lock_sticky); |
980 | debugfs_create_file(name: "qspl_pv_sleepy_lock_interval_ns" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_sleepy_lock_interval_ns); |
981 | debugfs_create_file(name: "qspl_pv_sleepy_lock_factor" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_sleepy_lock_factor); |
982 | debugfs_create_file(name: "qspl_pv_yield_prev" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_yield_prev); |
983 | debugfs_create_file(name: "qspl_pv_yield_sleepy_owner" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_yield_sleepy_owner); |
984 | debugfs_create_file(name: "qspl_pv_prod_head" , mode: 0600, parent: arch_debugfs_dir, NULL, fops: &fops_pv_prod_head); |
985 | } |
986 | |
987 | return 0; |
988 | } |
989 | device_initcall(spinlock_debugfs_init); |
990 | |