arch/x86/include/asm/preempt.h

   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
   8 DECLARE_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  */
  20 static __always_inline int preempt_count(void)
  21 {
  22         return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
  23 }
  24
  25 static __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
  54 static __always_inline void set_preempt_need_resched(void)
  55 {
  56         raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
  57 }
  58
  59 static __always_inline void clear_preempt_need_resched(void)
  60 {
  61         raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
  62 }
  63
  64 static __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
  73 static __always_inline void __preempt_count_add(int val)
  74 {
  75         raw_cpu_add_4(__preempt_count, val);
  76 }
  77
  78 static __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  */
  88 static __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  */
  96 static __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 */