include/linux/sched_clock.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * sched_clock.h: support for extending counters to full 64-bit ns counter
   4  */
   5 #ifndef LINUX_SCHED_CLOCK
   6 #define LINUX_SCHED_CLOCK
   7
   8 #include <linux/types.h>
   9
  10 #ifdef CONFIG_GENERIC_SCHED_CLOCK
  11 /**
  12  * struct clock_read_data - data required to read from sched_clock()
  13  *
  14  * @epoch_ns:           sched_clock() value at last update
  15  * @epoch_cyc:          Clock cycle value at last update.
  16  * @sched_clock_mask:   Bitmask for two's complement subtraction of non 64bit
  17  *                      clocks.
  18  * @read_sched_clock:   Current clock source (or dummy source when suspended).
  19  * @mult:               Multiplier for scaled math conversion.
  20  * @shift:              Shift value for scaled math conversion.
  21  *
  22  * Care must be taken when updating this structure; it is read by
  23  * some very hot code paths. It occupies <=40 bytes and, when combined
  24  * with the seqcount used to synchronize access, comfortably fits into
  25  * a 64 byte cache line.
  26  */
  27 struct clock_read_data {
  28         u64 epoch_ns;
  29         u64 epoch_cyc;
  30         u64 sched_clock_mask;
  31         u64 (*read_sched_clock)(void);
  32         u32 mult;
  33         u32 shift;
  34 };
  35
  36 extern struct clock_read_data *sched_clock_read_begin(unsigned int *seq);
  37 extern int sched_clock_read_retry(unsigned int seq);
  38
  39 extern void generic_sched_clock_init(void);
  40
  41 extern void sched_clock_register(u64 (*read)(void), int bits,
  42                                  unsigned long rate);
  43 #else
  44 static inline void generic_sched_clock_init(void) { }
  45
  46 static inline void sched_clock_register(u64 (*read)(void), int bits,
  47                                         unsigned long rate)
  48 {
  49 }
  50 #endif
  51
  52 #endif