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 mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
  12  * that think a non-zero value indicates we cannot preempt.
  13  */
  14 static __always_inline int preempt_count(void)
  15 {
  16         return __this_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
  17 }
  18
  19 static __always_inline void preempt_count_set(int pc)
  20 {
  21         __this_cpu_write_4(__preempt_count, pc);
  22 }
  23
  24 /*
  25  * must be macros to avoid header recursion hell
  26  */
  27 #define task_preempt_count(p) \
  28         (task_thread_info(p)->saved_preempt_count & ~PREEMPT_NEED_RESCHED)
  29
  30 #define init_task_preempt_count(p) do { \
  31         task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \
  32 } while (0)
  33
  34 #define init_idle_preempt_count(p, cpu) do { \
  35         task_thread_info(p)->saved_preempt_count = PREEMPT_ENABLED; \
  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         __this_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
  51 }
  52
  53 static __always_inline void clear_preempt_need_resched(void)
  54 {
  55         __this_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
  56 }
  57
  58 static __always_inline bool test_preempt_need_resched(void)
  59 {
  60         return !(__this_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         __this_cpu_add_4(__preempt_count, val);
  70 }
  71
  72 static __always_inline void __preempt_count_sub(int val)
  73 {
  74         __this_cpu_add_4(__preempt_count, -val);
  75 }
  76
  77 static __always_inline bool __preempt_count_dec_and_test(void)
  78 {
  79         GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), "e");
  80 }
  81
  82 /*
  83  * Returns true when we need to resched -- even if we can not.
  84  */
  85 static __always_inline bool need_resched(void)
  86 {
  87         return unlikely(test_preempt_need_resched());
  88 }
  89
  90 /*
  91  * Returns true when we need to resched and can (barring IRQ state).
  92  */
  93 static __always_inline bool should_resched(void)
  94 {
  95         return unlikely(!__this_cpu_read_4(__preempt_count));
  96 }
  97
  98 #endif /* __ASM_PREEMPT_H */