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
check_zero(void)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
spin_time_start(void)58 static inline u64 spin_time_start(void)
59 {
60 return xen_clocksource_read();
61 }
62
__spin_time_accum(u64 delta,u32 * array)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
spin_time_accum_spinning(u64 start)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
spin_time_accum_total(u64 start)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
spin_time_accum_blocked(u64 start)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
spin_time_start(void)102 static inline u64 spin_time_start(void)
103 {
104 return 0;
105 }
106
spin_time_accum_total(u64 start)107 static inline void spin_time_accum_total(u64 start)
108 {
109 }
spin_time_accum_spinning(u64 start)110 static inline void spin_time_accum_spinning(u64 start)
111 {
112 }
spin_time_accum_blocked(u64 start)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
xen_spin_is_locked(struct raw_spinlock * lock)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
xen_spin_is_contended(struct raw_spinlock * lock)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
xen_spin_trylock(struct raw_spinlock * lock)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 */
spinning_lock(struct xen_spinlock * xl)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 */
unspinning_lock(struct xen_spinlock * xl,struct xen_spinlock * prev)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
xen_spin_lock_slow(struct raw_spinlock * lock,bool irq_enable)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 unsigned long flags;
191 u64 start;
192
193 /* If kicker interrupts not initialized yet, just spin */
194 if (irq == -1)
195 return 0;
196
197 start = spin_time_start();
198
199 /* announce we're spinning */
200 prev = spinning_lock(xl);
201
202 flags = __raw_local_save_flags();
203 if (irq_enable) {
204 ADD_STATS(taken_slow_irqenable, 1);
205 raw_local_irq_enable();
206 }
207
208 ADD_STATS(taken_slow, 1);
209 ADD_STATS(taken_slow_nested, prev != NULL);
210
211 do {
212 /* clear pending */
213 xen_clear_irq_pending(irq);
214
215 /* check again make sure it didn't become free while
216 we weren't looking */
217 ret = xen_spin_trylock(lock);
218 if (ret) {
219 ADD_STATS(taken_slow_pickup, 1);
220
221 /*
222 * If we interrupted another spinlock while it
223 * was blocking, make sure it doesn't block
224 * without rechecking the lock.
225 */
226 if (prev != NULL)
227 xen_set_irq_pending(irq);
228 goto out;
229 }
230
231 /*
232 * Block until irq becomes pending. If we're
233 * interrupted at this point (after the trylock but
234 * before entering the block), then the nested lock
235 * handler guarantees that the irq will be left
236 * pending if there's any chance the lock became free;
237 * xen_poll_irq() returns immediately if the irq is
238 * pending.
239 */
240 xen_poll_irq(irq);
241 ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
242 } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
243
244 kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
245
246 out:
247 raw_local_irq_restore(flags);
248 unspinning_lock(xl, prev);
249 spin_time_accum_blocked(start);
250
251 return ret;
252 }
253
__xen_spin_lock(struct raw_spinlock * lock,bool irq_enable)254 static inline void __xen_spin_lock(struct raw_spinlock *lock, bool irq_enable)
255 {
256 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
257 unsigned timeout;
258 u8 oldval;
259 u64 start_spin;
260
261 ADD_STATS(taken, 1);
262
263 start_spin = spin_time_start();
264
265 do {
266 u64 start_spin_fast = spin_time_start();
267
268 timeout = TIMEOUT;
269
270 asm("1: xchgb %1,%0\n"
271 " testb %1,%1\n"
272 " jz 3f\n"
273 "2: rep;nop\n"
274 " cmpb $0,%0\n"
275 " je 1b\n"
276 " dec %2\n"
277 " jnz 2b\n"
278 "3:\n"
279 : "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
280 : "1" (1)
281 : "memory");
282
283 spin_time_accum_spinning(start_spin_fast);
284
285 } while (unlikely(oldval != 0 &&
286 (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));
287
288 spin_time_accum_total(start_spin);
289 }
290
xen_spin_lock(struct raw_spinlock * lock)291 static void xen_spin_lock(struct raw_spinlock *lock)
292 {
293 __xen_spin_lock(lock, false);
294 }
295
xen_spin_lock_flags(struct raw_spinlock * lock,unsigned long flags)296 static void xen_spin_lock_flags(struct raw_spinlock *lock, unsigned long flags)
297 {
298 __xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
299 }
300
xen_spin_unlock_slow(struct xen_spinlock * xl)301 static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
302 {
303 int cpu;
304
305 ADD_STATS(released_slow, 1);
306
307 for_each_online_cpu(cpu) {
308 /* XXX should mix up next cpu selection */
309 if (per_cpu(lock_spinners, cpu) == xl) {
310 ADD_STATS(released_slow_kicked, 1);
311 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
312 break;
313 }
314 }
315 }
316
xen_spin_unlock(struct raw_spinlock * lock)317 static void xen_spin_unlock(struct raw_spinlock *lock)
318 {
319 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
320
321 ADD_STATS(released, 1);
322
323 smp_wmb(); /* make sure no writes get moved after unlock */
324 xl->lock = 0; /* release lock */
325
326 /* make sure unlock happens before kick */
327 barrier();
328
329 if (unlikely(xl->spinners))
330 xen_spin_unlock_slow(xl);
331 }
332
dummy_handler(int irq,void * dev_id)333 static irqreturn_t dummy_handler(int irq, void *dev_id)
334 {
335 BUG();
336 return IRQ_HANDLED;
337 }
338
xen_init_lock_cpu(int cpu)339 void __cpuinit xen_init_lock_cpu(int cpu)
340 {
341 int irq;
342 const char *name;
343
344 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
345 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
346 cpu,
347 dummy_handler,
348 IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
349 name,
350 NULL);
351
352 if (irq >= 0) {
353 disable_irq(irq); /* make sure it's never delivered */
354 per_cpu(lock_kicker_irq, cpu) = irq;
355 }
356
357 printk("cpu %d spinlock event irq %d\n", cpu, irq);
358 }
359
xen_uninit_lock_cpu(int cpu)360 void xen_uninit_lock_cpu(int cpu)
361 {
362 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
363 }
364
xen_init_spinlocks(void)365 void __init xen_init_spinlocks(void)
366 {
367 pv_lock_ops.spin_is_locked = xen_spin_is_locked;
368 pv_lock_ops.spin_is_contended = xen_spin_is_contended;
369 pv_lock_ops.spin_lock = xen_spin_lock;
370 pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
371 pv_lock_ops.spin_trylock = xen_spin_trylock;
372 pv_lock_ops.spin_unlock = xen_spin_unlock;
373 }
374
375 #ifdef CONFIG_XEN_DEBUG_FS
376
377 static struct dentry *d_spin_debug;
378
xen_spinlock_debugfs(void)379 static int __init xen_spinlock_debugfs(void)
380 {
381 struct dentry *d_xen = xen_init_debugfs();
382
383 if (d_xen == NULL)
384 return -ENOMEM;
385
386 d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
387
388 debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
389
390 debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);
391
392 debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
393 debugfs_create_u32("taken_slow", 0444, d_spin_debug,
394 &spinlock_stats.taken_slow);
395 debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
396 &spinlock_stats.taken_slow_nested);
397 debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
398 &spinlock_stats.taken_slow_pickup);
399 debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
400 &spinlock_stats.taken_slow_spurious);
401 debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
402 &spinlock_stats.taken_slow_irqenable);
403
404 debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
405 debugfs_create_u32("released_slow", 0444, d_spin_debug,
406 &spinlock_stats.released_slow);
407 debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
408 &spinlock_stats.released_slow_kicked);
409
410 debugfs_create_u64("time_spinning", 0444, d_spin_debug,
411 &spinlock_stats.time_spinning);
412 debugfs_create_u64("time_blocked", 0444, d_spin_debug,
413 &spinlock_stats.time_blocked);
414 debugfs_create_u64("time_total", 0444, d_spin_debug,
415 &spinlock_stats.time_total);
416
417 xen_debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
418 spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
419 xen_debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
420 spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
421 xen_debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
422 spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
423
424 return 0;
425 }
426 fs_initcall(xen_spinlock_debugfs);
427
428 #endif /* CONFIG_XEN_DEBUG_FS */
429