1 /*
2 * Split spinlock implementation out into its own file, so it can be
3 * compiled in a FTRACE-compatible way.
4 */
5 #include <linux/kernel_stat.h>
6 #include <linux/spinlock.h>
7 #include <linux/debugfs.h>
8 #include <linux/log2.h>
9
10 #include <asm/paravirt.h>
11
12 #include <xen/interface/xen.h>
13 #include <xen/events.h>
14
15 #include "xen-ops.h"
16 #include "debugfs.h"
17
18 #ifdef CONFIG_XEN_DEBUG_FS
19 static struct xen_spinlock_stats
20 {
21 u64 taken;
22 u32 taken_slow;
23 u32 taken_slow_nested;
24 u32 taken_slow_pickup;
25 u32 taken_slow_spurious;
26 u32 taken_slow_irqenable;
27
28 u64 released;
29 u32 released_slow;
30 u32 released_slow_kicked;
31
32 #define HISTO_BUCKETS 30
33 u32 histo_spin_total[HISTO_BUCKETS+1];
34 u32 histo_spin_spinning[HISTO_BUCKETS+1];
35 u32 histo_spin_blocked[HISTO_BUCKETS+1];
36
37 u64 time_total;
38 u64 time_spinning;
39 u64 time_blocked;
40 } spinlock_stats;
41
42 static u8 zero_stats;
43
44 static unsigned lock_timeout = 1 << 10;
45 #define TIMEOUT lock_timeout
46
47 static inline void check_zero(void)
48 {
49 if (unlikely(zero_stats)) {
50 memset(&spinlock_stats, 0, sizeof(spinlock_stats));
51 zero_stats = 0;
52 }
53 }
54
55 #define ADD_STATS(elem, val) \
56 do { check_zero(); spinlock_stats.elem += (val); } while(0)
57
58 static inline u64 spin_time_start(void)
59 {
60 return xen_clocksource_read();
61 }
62
63 static void __spin_time_accum(u64 delta, u32 *array)
64 {
65 unsigned index = ilog2(delta);
66
67 check_zero();
68
69 if (index < HISTO_BUCKETS)
70 array[index]++;
71 else
72 array[HISTO_BUCKETS]++;
73 }
74
75 static inline void spin_time_accum_spinning(u64 start)
76 {
77 u32 delta = xen_clocksource_read() - start;
78
79 __spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
80 spinlock_stats.time_spinning += delta;
81 }
82
83 static inline void spin_time_accum_total(u64 start)
84 {
85 u32 delta = xen_clocksource_read() - start;
86
87 __spin_time_accum(delta, spinlock_stats.histo_spin_total);
88 spinlock_stats.time_total += delta;
89 }
90
91 static inline void spin_time_accum_blocked(u64 start)
92 {
93 u32 delta = xen_clocksource_read() - start;
94
95 __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
96 spinlock_stats.time_blocked += delta;
97 }
98 #else /* !CONFIG_XEN_DEBUG_FS */
99 #define TIMEOUT (1 << 10)
100 #define ADD_STATS(elem, val) do { (void)(val); } while(0)
101
102 static inline u64 spin_time_start(void)
103 {
104 return 0;
105 }
106
107 static inline void spin_time_accum_total(u64 start)
108 {
109 }
110 static inline void spin_time_accum_spinning(u64 start)
111 {
112 }
113 static inline void spin_time_accum_blocked(u64 start)
114 {
115 }
116 #endif /* CONFIG_XEN_DEBUG_FS */
117
118 struct xen_spinlock {
119 unsigned char lock; /* 0 -> free; 1 -> locked */
120 unsigned short spinners; /* count of waiting cpus */
121 };
122
123 static int xen_spin_is_locked(struct raw_spinlock *lock)
124 {
125 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
126
127 return xl->lock != 0;
128 }
129
130 static int xen_spin_is_contended(struct raw_spinlock *lock)
131 {
132 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
133
134 /* Not strictly true; this is only the count of contended
135 lock-takers entering the slow path. */
136 return xl->spinners != 0;
137 }
138
139 static int xen_spin_trylock(struct raw_spinlock *lock)
140 {
141 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
142 u8 old = 1;
143
144 asm("xchgb %b0,%1"
145 : "+q" (old), "+m" (xl->lock) : : "memory");
146
147 return old == 0;
148 }
149
150 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
151 static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
152
153 /*
154 * Mark a cpu as interested in a lock. Returns the CPU's previous
155 * lock of interest, in case we got preempted by an interrupt.
156 */
157 static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
158 {
159 struct xen_spinlock *prev;
160
161 prev = __get_cpu_var(lock_spinners);
162 __get_cpu_var(lock_spinners) = xl;
163
164 wmb(); /* set lock of interest before count */
165
166 asm(LOCK_PREFIX " incw %0"
167 : "+m" (xl->spinners) : : "memory");
168
169 return prev;
170 }
171
172 /*
173 * Mark a cpu as no longer interested in a lock. Restores previous
174 * lock of interest (NULL for none).
175 */
176 static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock *prev)
177 {
178 asm(LOCK_PREFIX " decw %0"
179 : "+m" (xl->spinners) : : "memory");
180 wmb(); /* decrement count before restoring lock */
181 __get_cpu_var(lock_spinners) = prev;
182 }
183
184 static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enable)
185 {
186 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
187 struct xen_spinlock *prev;
188 int irq = __get_cpu_var(lock_kicker_irq);
189 int ret;
190 u64 start;
191
192 /* If kicker interrupts not initialized yet, just spin */
193 if (irq == -1)
194 return 0;
195
196 start = spin_time_start();
197
198 /* announce we're spinning */
199 prev = spinning_lock(xl);
200
201 ADD_STATS(taken_slow, 1);
202 ADD_STATS(taken_slow_nested, prev != NULL);
203
204 do {
205 unsigned long flags;
206
207 /* clear pending */
208 xen_clear_irq_pending(irq);
209
210 /* check again make sure it didn't become free while
211 we weren't looking */
212 ret = xen_spin_trylock(lock);
213 if (ret) {
214 ADD_STATS(taken_slow_pickup, 1);
215
216 /*
217 * If we interrupted another spinlock while it
218 * was blocking, make sure it doesn't block
219 * without rechecking the lock.
220 */
221 if (prev != NULL)
222 xen_set_irq_pending(irq);
223 goto out;
224 }
225
226 flags = __raw_local_save_flags();
227 if (irq_enable) {
228 ADD_STATS(taken_slow_irqenable, 1);
229 raw_local_irq_enable();
230 }
231
232 /*
233 * Block until irq becomes pending. If we're
234 * interrupted at this point (after the trylock but
235 * before entering the block), then the nested lock
236 * handler guarantees that the irq will be left
237 * pending if there's any chance the lock became free;
238 * xen_poll_irq() returns immediately if the irq is
239 * pending.
240 */
241 xen_poll_irq(irq);
242
243 raw_local_irq_restore(flags);
244
245 ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
246 } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
247
248 kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
249
250 out:
251 unspinning_lock(xl, prev);
252 spin_time_accum_blocked(start);
253
254 return ret;
255 }
256
257 static inline void __xen_spin_lock(struct raw_spinlock *lock, bool irq_enable)
258 {
259 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
260 unsigned timeout;
261 u8 oldval;
262 u64 start_spin;
263
264 ADD_STATS(taken, 1);
265
266 start_spin = spin_time_start();
267
268 do {
269 u64 start_spin_fast = spin_time_start();
270
271 timeout = TIMEOUT;
272
273 asm("1: xchgb %1,%0\n"
274 " testb %1,%1\n"
275 " jz 3f\n"
276 "2: rep;nop\n"
277 " cmpb $0,%0\n"
278 " je 1b\n"
279 " dec %2\n"
280 " jnz 2b\n"
281 "3:\n"
282 : "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
283 : "1" (1)
284 : "memory");
285
286 spin_time_accum_spinning(start_spin_fast);
287
288 } while (unlikely(oldval != 0 &&
289 (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));
290
291 spin_time_accum_total(start_spin);
292 }
293
294 static void xen_spin_lock(struct raw_spinlock *lock)
295 {
296 __xen_spin_lock(lock, false);
297 }
298
299 static void xen_spin_lock_flags(struct raw_spinlock *lock, unsigned long flags)
300 {
301 __xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
302 }
303
304 static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
305 {
306 int cpu;
307
308 ADD_STATS(released_slow, 1);
309
310 for_each_online_cpu(cpu) {
311 /* XXX should mix up next cpu selection */
312 if (per_cpu(lock_spinners, cpu) == xl) {
313 ADD_STATS(released_slow_kicked, 1);
314 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
315 break;
316 }
317 }
318 }
319
320 static void xen_spin_unlock(struct raw_spinlock *lock)
321 {
322 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
323
324 ADD_STATS(released, 1);
325
326 smp_wmb(); /* make sure no writes get moved after unlock */
327 xl->lock = 0; /* release lock */
328
329 /*
330 * Make sure unlock happens before checking for waiting
331 * spinners. We need a strong barrier to enforce the
332 * write-read ordering to different memory locations, as the
333 * CPU makes no implied guarantees about their ordering.
334 */
335 mb();
336
337 if (unlikely(xl->spinners))
338 xen_spin_unlock_slow(xl);
339 }
340
341 static irqreturn_t dummy_handler(int irq, void *dev_id)
342 {
343 BUG();
344 return IRQ_HANDLED;
345 }
346
347 void __cpuinit xen_init_lock_cpu(int cpu)
348 {
349 int irq;
350 const char *name;
351
352 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
353 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
354 cpu,
355 dummy_handler,
356 IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
357 name,
358 NULL);
359
360 if (irq >= 0) {
361 disable_irq(irq); /* make sure it's never delivered */
362 per_cpu(lock_kicker_irq, cpu) = irq;
363 }
364
365 printk("cpu %d spinlock event irq %d\n", cpu, irq);
366 }
367
368 void xen_uninit_lock_cpu(int cpu)
369 {
370 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
371 }
372
373 void __init xen_init_spinlocks(void)
374 {
375 pv_lock_ops.spin_is_locked = xen_spin_is_locked;
376 pv_lock_ops.spin_is_contended = xen_spin_is_contended;
377 pv_lock_ops.spin_lock = xen_spin_lock;
378 pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
379 pv_lock_ops.spin_trylock = xen_spin_trylock;
380 pv_lock_ops.spin_unlock = xen_spin_unlock;
381 }
382
383 #ifdef CONFIG_XEN_DEBUG_FS
384
385 static struct dentry *d_spin_debug;
386
387 static int __init xen_spinlock_debugfs(void)
388 {
389 struct dentry *d_xen = xen_init_debugfs();
390
391 if (d_xen == NULL)
392 return -ENOMEM;
393
394 d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
395
396 debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
397
398 debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);
399
400 debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
401 debugfs_create_u32("taken_slow", 0444, d_spin_debug,
402 &spinlock_stats.taken_slow);
403 debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
404 &spinlock_stats.taken_slow_nested);
405 debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
406 &spinlock_stats.taken_slow_pickup);
407 debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
408 &spinlock_stats.taken_slow_spurious);
409 debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
410 &spinlock_stats.taken_slow_irqenable);
411
412 debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
413 debugfs_create_u32("released_slow", 0444, d_spin_debug,
414 &spinlock_stats.released_slow);
415 debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
416 &spinlock_stats.released_slow_kicked);
417
418 debugfs_create_u64("time_spinning", 0444, d_spin_debug,
419 &spinlock_stats.time_spinning);
420 debugfs_create_u64("time_blocked", 0444, d_spin_debug,
421 &spinlock_stats.time_blocked);
422 debugfs_create_u64("time_total", 0444, d_spin_debug,
423 &spinlock_stats.time_total);
424
425 xen_debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
426 spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
427 xen_debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
428 spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
429 xen_debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
430 spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
431
432 return 0;
433 }
434 fs_initcall(xen_spinlock_debugfs);
435
436 #endif /* CONFIG_XEN_DEBUG_FS */
437
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