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         raw_cpu_write_4(__preempt_count, pc);
  28 }
  29
  30 /*
  31  * must be macros to avoid header recursion hell
  32  */
  33 #define init_task_preempt_count(p) do { } while (0)
  34
  35 #define init_idle_preempt_count(p, cpu) do { \
  36         per_cpu(__preempt_count, (cpu)) = PREEMPT_ENABLED; \
  37 } while (0)
  38
  39 /*
  40  * We fold the NEED_RESCHED bit into the preempt count such that
  41  * preempt_enable() can decrement and test for needing to reschedule with a
  42  * single instruction.
  43  *
  44  * We invert the actual bit, so that when the decrement hits 0 we know we both
  45  * need to resched (the bit is cleared) and can resched (no preempt count).
  46  */
  47
  48 static __always_inline void set_preempt_need_resched(void)
  49 {
  50         raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
  51 }
  52
  53 static __always_inline void clear_preempt_need_resched(void)
  54 {
  55         raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
  56 }
  57
  58 static __always_inline bool test_preempt_need_resched(void)
  59 {
  60         return !(raw_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
  61 }
  62
  63 /*
  64  * The various preempt_count add/sub methods
  65  */
  66
  67 static __always_inline void __preempt_count_add(int val)
  68 {
  69         raw_cpu_add_4(__preempt_count, val);
  70 }
  71
  72 static __always_inline void __preempt_count_sub(int val)
  73 {
  74         raw_cpu_add_4(__preempt_count, -val);
  75 }
  76
  77 /*
  78  * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
  79  * a decrement which hits zero means we have no preempt_count and should
  80  * reschedule.
  81  */
  82 static __always_inline bool __preempt_count_dec_and_test(void)
  83 {
  84         GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), "e");
  85 }
  86
  87 /*
  88  * Returns true when we need to resched and can (barring IRQ state).
  89  */
  90 static __always_inline bool should_resched(int preempt_offset)
  91 {
  92         return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
  93 }
  94
  95 #ifdef CONFIG_PREEMPT
  96   extern asmlinkage void ___preempt_schedule(void);
  97 # define __preempt_schedule() asm ("call ___preempt_schedule")
  98   extern asmlinkage void preempt_schedule(void);
  99   extern asmlinkage void ___preempt_schedule_notrace(void);
 100 # define __preempt_schedule_notrace() asm ("call ___preempt_schedule_notrace")
 101   extern asmlinkage void preempt_schedule_notrace(void);
 102 #endif
 103
 104 #endif /* __ASM_PREEMPT_H */