Linux Kernel  3.7.1
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spinlock_64.c
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1 /*
2  * Copyright 2011 Tilera Corporation. All Rights Reserved.
3  *
4  * This program is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU General Public License
6  * as published by the Free Software Foundation, version 2.
7  *
8  * This program is distributed in the hope that it will be useful, but
9  * WITHOUT ANY WARRANTY; without even the implied warranty of
10  * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11  * NON INFRINGEMENT. See the GNU General Public License for
12  * more details.
13  */
14 
15 #include <linux/spinlock.h>
16 #include <linux/module.h>
17 #include <asm/processor.h>
18 
19 #include "spinlock_common.h"
20 
21 /*
22  * Read the spinlock value without allocating in our cache and without
23  * causing an invalidation to another cpu with a copy of the cacheline.
24  * This is important when we are spinning waiting for the lock.
25  */
26 static inline u32 arch_spin_read_noalloc(void *lock)
27 {
28  return atomic_cmpxchg((atomic_t *)lock, -1, -1);
29 }
30 
31 /*
32  * Wait until the high bits (current) match my ticket.
33  * If we notice the overflow bit set on entry, we clear it.
34  */
35 void arch_spin_lock_slow(arch_spinlock_t *lock, u32 my_ticket)
36 {
37  if (unlikely(my_ticket & __ARCH_SPIN_NEXT_OVERFLOW)) {
38  __insn_fetchand4(&lock->lock, ~__ARCH_SPIN_NEXT_OVERFLOW);
39  my_ticket &= ~__ARCH_SPIN_NEXT_OVERFLOW;
40  }
41 
42  for (;;) {
43  u32 val = arch_spin_read_noalloc(lock);
44  u32 delta = my_ticket - arch_spin_current(val);
45  if (delta == 0)
46  return;
47  relax((128 / CYCLES_PER_RELAX_LOOP) * delta);
48  }
49 }
51 
52 /*
53  * Check the lock to see if it is plausible, and try to get it with cmpxchg().
54  */
56 {
57  u32 val = arch_spin_read_noalloc(lock);
58  if (unlikely(arch_spin_current(val) != arch_spin_next(val)))
59  return 0;
60  return cmpxchg(&lock->lock, val, (val + 1) & ~__ARCH_SPIN_NEXT_OVERFLOW)
61  == val;
62 }
64 
66 {
67  u32 iterations = 0;
68  while (arch_spin_is_locked(lock))
69  delay_backoff(iterations++);
70 }
72 
73 /*
74  * If the read lock fails due to a writer, we retry periodically
75  * until the value is positive and we write our incremented reader count.
76  */
78 {
79  u32 val;
80  int iterations = 0;
81  do {
82  delay_backoff(iterations++);
83  val = __insn_fetchaddgez4(&rw->lock, 1);
84  } while (unlikely(arch_write_val_locked(val)));
85 }
87 
88 /*
89  * If we failed because there were readers, clear the "writer" bit
90  * so we don't block additional readers. Otherwise, there was another
91  * writer anyway, so our "fetchor" made no difference. Then wait,
92  * issuing periodic fetchor instructions, till we get the lock.
93  */
95 {
96  int iterations = 0;
97  do {
98  if (!arch_write_val_locked(val))
99  val = __insn_fetchand4(&rw->lock, ~__WRITE_LOCK_BIT);
100  delay_backoff(iterations++);
101  val = __insn_fetchor4(&rw->lock, __WRITE_LOCK_BIT);
102  } while (val != 0);
103 }