arch/x86/xen/spinlock.c

   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 #include <linux/gfp.h>
  10 #include <linux/slab.h>
  11
  12 #include <asm/paravirt.h>
  13
  14 #include <xen/interface/xen.h>
  15 #include <xen/events.h>
  16
  17 #include "xen-ops.h"
  18 #include "debugfs.h"
  19
  20 #ifdef CONFIG_XEN_DEBUG_FS
  21 static struct xen_spinlock_stats
  22 {
  23         u64 taken;
  24         u32 taken_slow;
  25         u32 taken_slow_nested;
  26         u32 taken_slow_pickup;
  27         u32 taken_slow_spurious;
  28         u32 taken_slow_irqenable;
  29
  30         u64 released;
  31         u32 released_slow;
  32         u32 released_slow_kicked;
  33
  34 #define HISTO_BUCKETS   30
  35         u32 histo_spin_total[HISTO_BUCKETS+1];
  36         u32 histo_spin_spinning[HISTO_BUCKETS+1];
  37         u32 histo_spin_blocked[HISTO_BUCKETS+1];
  38
  39         u64 time_total;
  40         u64 time_spinning;
  41         u64 time_blocked;
  42 } spinlock_stats;
  43
  44 static u8 zero_stats;
  45
  46 static unsigned lock_timeout = 1 << 10;
  47 #define TIMEOUT lock_timeout
  48
  49 static inline void check_zero(void)
  50 {
  51         if (unlikely(zero_stats)) {
  52                 memset(&spinlock_stats, 0, sizeof(spinlock_stats));
  53                 zero_stats = 0;
  54         }
  55 }
  56
  57 #define ADD_STATS(elem, val)                    \
  58         do { check_zero(); spinlock_stats.elem += (val); } while(0)
  59
  60 static inline u64 spin_time_start(void)
  61 {
  62         return xen_clocksource_read();
  63 }
  64
  65 static void __spin_time_accum(u64 delta, u32 *array)
  66 {
  67         unsigned index = ilog2(delta);
  68
  69         check_zero();
  70
  71         if (index < HISTO_BUCKETS)
  72                 array[index]++;
  73         else
  74                 array[HISTO_BUCKETS]++;
  75 }
  76
  77 static inline void spin_time_accum_spinning(u64 start)
  78 {
  79         u32 delta = xen_clocksource_read() - start;
  80
  81         __spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
  82         spinlock_stats.time_spinning += delta;
  83 }
  84
  85 static inline void spin_time_accum_total(u64 start)
  86 {
  87         u32 delta = xen_clocksource_read() - start;
  88
  89         __spin_time_accum(delta, spinlock_stats.histo_spin_total);
  90         spinlock_stats.time_total += delta;
  91 }
  92
  93 static inline void spin_time_accum_blocked(u64 start)
  94 {
  95         u32 delta = xen_clocksource_read() - start;
  96
  97         __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
  98         spinlock_stats.time_blocked += delta;
  99 }
 100 #else  /* !CONFIG_XEN_DEBUG_FS */
 101 #define TIMEOUT                 (1 << 10)
 102 #define ADD_STATS(elem, val)    do { (void)(val); } while(0)
 103
 104 static inline u64 spin_time_start(void)
 105 {
 106         return 0;
 107 }
 108
 109 static inline void spin_time_accum_total(u64 start)
 110 {
 111 }
 112 static inline void spin_time_accum_spinning(u64 start)
 113 {
 114 }
 115 static inline void spin_time_accum_blocked(u64 start)
 116 {
 117 }
 118 #endif  /* CONFIG_XEN_DEBUG_FS */
 119
 120 /*
 121  * Size struct xen_spinlock so it's the same as arch_spinlock_t.
 122  */
 123 #if NR_CPUS < 256
 124 typedef u8 xen_spinners_t;
 125 # define inc_spinners(xl) \
 126         asm(LOCK_PREFIX " incb %0" : "+m" ((xl)->spinners) : : "memory");
 127 # define dec_spinners(xl) \
 128         asm(LOCK_PREFIX " decb %0" : "+m" ((xl)->spinners) : : "memory");
 129 #else
 130 typedef u16 xen_spinners_t;
 131 # define inc_spinners(xl) \
 132         asm(LOCK_PREFIX " incw %0" : "+m" ((xl)->spinners) : : "memory");
 133 # define dec_spinners(xl) \
 134         asm(LOCK_PREFIX " decw %0" : "+m" ((xl)->spinners) : : "memory");
 135 #endif
 136
 137 struct xen_spinlock {
 138         unsigned char lock;             /* 0 -> free; 1 -> locked */
 139         xen_spinners_t spinners;        /* count of waiting cpus */
 140 };
 141
 142 static int xen_spin_is_locked(struct arch_spinlock *lock)
 143 {
 144         struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 145
 146         return xl->lock != 0;
 147 }
 148
 149 static int xen_spin_is_contended(struct arch_spinlock *lock)
 150 {
 151         struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 152
 153         /* Not strictly true; this is only the count of contended
 154            lock-takers entering the slow path. */
 155         return xl->spinners != 0;
 156 }
 157
 158 static int xen_spin_trylock(struct arch_spinlock *lock)
 159 {
 160         struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 161         u8 old = 1;
 162
 163         asm("xchgb %b0,%1"
 164             : "+q" (old), "+m" (xl->lock) : : "memory");
 165
 166         return old == 0;
 167 }
 168
 169 static DEFINE_PER_CPU(char *, irq_name);
 170 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
 171 static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
 172
 173 /*
 174  * Mark a cpu as interested in a lock.  Returns the CPU's previous
 175  * lock of interest, in case we got preempted by an interrupt.
 176  */
 177 static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
 178 {
 179         struct xen_spinlock *prev;
 180
 181         prev = __this_cpu_read(lock_spinners);
 182         __this_cpu_write(lock_spinners, xl);
 183
 184         wmb();                  /* set lock of interest before count */
 185
 186         inc_spinners(xl);
 187
 188         return prev;
 189 }
 190
 191 /*
 192  * Mark a cpu as no longer interested in a lock.  Restores previous
 193  * lock of interest (NULL for none).
 194  */
 195 static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock *prev)
 196 {
 197         dec_spinners(xl);
 198         wmb();                  /* decrement count before restoring lock */
 199         __this_cpu_write(lock_spinners, prev);
 200 }
 201
 202 static noinline int xen_spin_lock_slow(struct arch_spinlock *lock, bool irq_enable)
 203 {
 204         struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 205         struct xen_spinlock *prev;
 206         int irq = __this_cpu_read(lock_kicker_irq);
 207         int ret;
 208         u64 start;
 209
 210         /* If kicker interrupts not initialized yet, just spin */
 211         if (irq == -1)
 212                 return 0;
 213
 214         start = spin_time_start();
 215
 216         /* announce we're spinning */
 217         prev = spinning_lock(xl);
 218
 219         ADD_STATS(taken_slow, 1);
 220         ADD_STATS(taken_slow_nested, prev != NULL);
 221
 222         do {
 223                 unsigned long flags;
 224
 225                 /* clear pending */
 226                 xen_clear_irq_pending(irq);
 227
 228                 /* check again make sure it didn't become free while
 229                    we weren't looking  */
 230                 ret = xen_spin_trylock(lock);
 231                 if (ret) {
 232                         ADD_STATS(taken_slow_pickup, 1);
 233
 234                         /*
 235                          * If we interrupted another spinlock while it
 236                          * was blocking, make sure it doesn't block
 237                          * without rechecking the lock.
 238                          */
 239                         if (prev != NULL)
 240                                 xen_set_irq_pending(irq);
 241                         goto out;
 242                 }
 243
 244                 flags = arch_local_save_flags();
 245                 if (irq_enable) {
 246                         ADD_STATS(taken_slow_irqenable, 1);
 247                         raw_local_irq_enable();
 248                 }
 249
 250                 /*
 251                  * Block until irq becomes pending.  If we're
 252                  * interrupted at this point (after the trylock but
 253                  * before entering the block), then the nested lock
 254                  * handler guarantees that the irq will be left
 255                  * pending if there's any chance the lock became free;
 256                  * xen_poll_irq() returns immediately if the irq is
 257                  * pending.
 258                  */
 259                 xen_poll_irq(irq);
 260
 261                 raw_local_irq_restore(flags);
 262
 263                 ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
 264         } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
 265
 266         kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
 267
 268 out:
 269         unspinning_lock(xl, prev);
 270         spin_time_accum_blocked(start);
 271
 272         return ret;
 273 }
 274
 275 static inline void __xen_spin_lock(struct arch_spinlock *lock, bool irq_enable)
 276 {
 277         struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 278         unsigned timeout;
 279         u8 oldval;
 280         u64 start_spin;
 281
 282         ADD_STATS(taken, 1);
 283
 284         start_spin = spin_time_start();
 285
 286         do {
 287                 u64 start_spin_fast = spin_time_start();
 288
 289                 timeout = TIMEOUT;
 290
 291                 asm("1: xchgb %1,%0\n"
 292                     "   testb %1,%1\n"
 293                     "   jz 3f\n"
 294                     "2: rep;nop\n"
 295                     "   cmpb $0,%0\n"
 296                     "   je 1b\n"
 297                     "   dec %2\n"
 298                     "   jnz 2b\n"
 299                     "3:\n"
 300                     : "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
 301                     : "1" (1)
 302                     : "memory");
 303
 304                 spin_time_accum_spinning(start_spin_fast);
 305
 306         } while (unlikely(oldval != 0 &&
 307                           (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));
 308
 309         spin_time_accum_total(start_spin);
 310 }
 311
 312 static void xen_spin_lock(struct arch_spinlock *lock)
 313 {
 314         __xen_spin_lock(lock, false);
 315 }
 316
 317 static void xen_spin_lock_flags(struct arch_spinlock *lock, unsigned long flags)
 318 {
 319         __xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
 320 }
 321
 322 static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
 323 {
 324         int cpu;
 325
 326         ADD_STATS(released_slow, 1);
 327
 328         for_each_online_cpu(cpu) {
 329                 /* XXX should mix up next cpu selection */
 330                 if (per_cpu(lock_spinners, cpu) == xl) {
 331                         ADD_STATS(released_slow_kicked, 1);
 332                         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
 333                 }
 334         }
 335 }
 336
 337 static void xen_spin_unlock(struct arch_spinlock *lock)
 338 {
 339         struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 340
 341         ADD_STATS(released, 1);
 342
 343         smp_wmb();              /* make sure no writes get moved after unlock */
 344         xl->lock = 0;           /* release lock */
 345
 346         /*
 347          * Make sure unlock happens before checking for waiting
 348          * spinners.  We need a strong barrier to enforce the
 349          * write-read ordering to different memory locations, as the
 350          * CPU makes no implied guarantees about their ordering.
 351          */
 352         mb();
 353
 354         if (unlikely(xl->spinners))
 355                 xen_spin_unlock_slow(xl);
 356 }
 357
 358 static irqreturn_t dummy_handler(int irq, void *dev_id)
 359 {
 360         BUG();
 361         return IRQ_HANDLED;
 362 }
 363
 364 void __cpuinit xen_init_lock_cpu(int cpu)
 365 {
 366         int irq;
 367         char *name;
 368
 369         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
 370              cpu, per_cpu(lock_kicker_irq, cpu));
 371
 372         /*
 373          * See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
 374          * (xen: disable PV spinlocks on HVM)
 375          */
 376         if (xen_hvm_domain())
 377                 return;
 378
 379         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
 380         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
 381                                      cpu,
 382                                      dummy_handler,
 383                                      IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 384                                      name,
 385                                      NULL);
 386
 387         if (irq >= 0) {
 388                 disable_irq(irq); /* make sure it's never delivered */
 389                 per_cpu(lock_kicker_irq, cpu) = irq;
 390                 per_cpu(irq_name, cpu) = name;
 391         }
 392
 393         printk("cpu %d spinlock event irq %d\n", cpu, irq);
 394 }
 395
 396 void xen_uninit_lock_cpu(int cpu)
 397 {
 398         /*
 399          * See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
 400          * (xen: disable PV spinlocks on HVM)
 401          */
 402         if (xen_hvm_domain())
 403                 return;
 404
 405         unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 406         per_cpu(lock_kicker_irq, cpu) = -1;
 407         kfree(per_cpu(irq_name, cpu));
 408         per_cpu(irq_name, cpu) = NULL;
 409 }
 410
 411 void __init xen_init_spinlocks(void)
 412 {
 413         /*
 414          * See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
 415          * (xen: disable PV spinlocks on HVM)
 416          */
 417         if (xen_hvm_domain())
 418                 return;
 419
 420         BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));
 421
 422         pv_lock_ops.spin_is_locked = xen_spin_is_locked;
 423         pv_lock_ops.spin_is_contended = xen_spin_is_contended;
 424         pv_lock_ops.spin_lock = xen_spin_lock;
 425         pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
 426         pv_lock_ops.spin_trylock = xen_spin_trylock;
 427         pv_lock_ops.spin_unlock = xen_spin_unlock;
 428 }
 429
 430 #ifdef CONFIG_XEN_DEBUG_FS
 431
 432 static struct dentry *d_spin_debug;
 433
 434 static int __init xen_spinlock_debugfs(void)
 435 {
 436         struct dentry *d_xen = xen_init_debugfs();
 437
 438         if (d_xen == NULL)
 439                 return -ENOMEM;
 440
 441         d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
 442
 443         debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
 444
 445         debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);
 446
 447         debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
 448         debugfs_create_u32("taken_slow", 0444, d_spin_debug,
 449                            &spinlock_stats.taken_slow);
 450         debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
 451                            &spinlock_stats.taken_slow_nested);
 452         debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
 453                            &spinlock_stats.taken_slow_pickup);
 454         debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
 455                            &spinlock_stats.taken_slow_spurious);
 456         debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
 457                            &spinlock_stats.taken_slow_irqenable);
 458
 459         debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
 460         debugfs_create_u32("released_slow", 0444, d_spin_debug,
 461                            &spinlock_stats.released_slow);
 462         debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
 463                            &spinlock_stats.released_slow_kicked);
 464
 465         debugfs_create_u64("time_spinning", 0444, d_spin_debug,
 466                            &spinlock_stats.time_spinning);
 467         debugfs_create_u64("time_blocked", 0444, d_spin_debug,
 468                            &spinlock_stats.time_blocked);
 469         debugfs_create_u64("time_total", 0444, d_spin_debug,
 470                            &spinlock_stats.time_total);
 471
 472         debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
 473                                 spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
 474         debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
 475                                 spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
 476         debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
 477                                 spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
 478
 479         return 0;
 480 }
 481 fs_initcall(xen_spinlock_debugfs);
 482
 483 #endif  /* CONFIG_XEN_DEBUG_FS */