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Linux kernel mirror (for testing)
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linux
1#ifndef __ASM_PREEMPT_H
2#define __ASM_PREEMPT_H
3
4#include <asm/rmwcc.h>
5#include <asm/percpu.h>
6#include <linux/thread_info.h>
7
8DECLARE_PER_CPU(int, __preempt_count);
9
10/*
11 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
12 * that a decrement hitting 0 means we can and should reschedule.
13 */
14#define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED)
15
16/*
17 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
18 * that think a non-zero value indicates we cannot preempt.
19 */
20static __always_inline int preempt_count(void)
21{
22 return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
23}
24
25static __always_inline void preempt_count_set(int pc)
26{
27 int old, new;
28
29 do {
30 old = raw_cpu_read_4(__preempt_count);
31 new = (old & PREEMPT_NEED_RESCHED) |
32 (pc & ~PREEMPT_NEED_RESCHED);
33 } while (raw_cpu_cmpxchg_4(__preempt_count, old, new) != old);
34}
35
36/*
37 * must be macros to avoid header recursion hell
38 */
39#define init_task_preempt_count(p) do { } while (0)
40
41#define init_idle_preempt_count(p, cpu) do { \
42 per_cpu(__preempt_count, (cpu)) = PREEMPT_ENABLED; \
43} while (0)
44
45/*
46 * We fold the NEED_RESCHED bit into the preempt count such that
47 * preempt_enable() can decrement and test for needing to reschedule with a
48 * single instruction.
49 *
50 * We invert the actual bit, so that when the decrement hits 0 we know we both
51 * need to resched (the bit is cleared) and can resched (no preempt count).
52 */
53
54static __always_inline void set_preempt_need_resched(void)
55{
56 raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
57}
58
59static __always_inline void clear_preempt_need_resched(void)
60{
61 raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
62}
63
64static __always_inline bool test_preempt_need_resched(void)
65{
66 return !(raw_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
67}
68
69/*
70 * The various preempt_count add/sub methods
71 */
72
73static __always_inline void __preempt_count_add(int val)
74{
75 raw_cpu_add_4(__preempt_count, val);
76}
77
78static __always_inline void __preempt_count_sub(int val)
79{
80 raw_cpu_add_4(__preempt_count, -val);
81}
82
83/*
84 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
85 * a decrement which hits zero means we have no preempt_count and should
86 * reschedule.
87 */
88static __always_inline bool __preempt_count_dec_and_test(void)
89{
90 GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), e);
91}
92
93/*
94 * Returns true when we need to resched and can (barring IRQ state).
95 */
96static __always_inline bool should_resched(int preempt_offset)
97{
98 return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
99}
100
101#ifdef CONFIG_PREEMPT
102 extern asmlinkage void ___preempt_schedule(void);
103# define __preempt_schedule() \
104({ \
105 register void *__sp asm(_ASM_SP); \
106 asm volatile ("call ___preempt_schedule" : "+r"(__sp)); \
107})
108
109 extern asmlinkage void preempt_schedule(void);
110 extern asmlinkage void ___preempt_schedule_notrace(void);
111# define __preempt_schedule_notrace() \
112({ \
113 register void *__sp asm(_ASM_SP); \
114 asm volatile ("call ___preempt_schedule_notrace" : "+r"(__sp)); \
115})
116 extern asmlinkage void preempt_schedule_notrace(void);
117#endif
118
119#endif /* __ASM_PREEMPT_H */