blob: 431793e5d4846f23bf5947f933fdaf9f5ae1987a [file] [log] [blame]
H. Peter Anvin1965aae2008-10-22 22:26:29 -07001#ifndef _ASM_X86_TIMER_H
2#define _ASM_X86_TIMER_H
Linus Torvalds1da177e2005-04-16 15:20:36 -07003#include <linux/init.h>
Shaohua Lic3c433e2005-09-03 15:57:07 -07004#include <linux/pm.h>
Guillaume Chazarain53d517c2008-01-30 13:30:06 +01005#include <linux/percpu.h>
Ingo Molnar8e6dafd2009-02-23 00:34:39 +01006#include <linux/interrupt.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07007
Linus Torvalds1da177e2005-04-16 15:20:36 -07008#define TICK_SIZE (tick_nsec / 1000)
Zachary Amsden6cb9a832007-03-05 00:30:35 -08009
Zachary Amsden6cb9a832007-03-05 00:30:35 -080010unsigned long long native_sched_clock(void);
Stephen Rothwell25c1a412009-03-30 11:10:27 +110011extern int recalibrate_cpu_khz(void);
Jaswinder Singhcc038492008-07-21 21:52:51 +053012
13extern int no_timer_check;
Linus Torvalds1da177e2005-04-16 15:20:36 -070014
Guillaume Chazarain53d517c2008-01-30 13:30:06 +010015/* Accelerators for sched_clock()
Jeremy Fitzhardinge688340e2007-07-17 18:37:04 -070016 * convert from cycles(64bits) => nanoseconds (64bits)
17 * basic equation:
18 * ns = cycles / (freq / ns_per_sec)
19 * ns = cycles * (ns_per_sec / freq)
20 * ns = cycles * (10^9 / (cpu_khz * 10^3))
21 * ns = cycles * (10^6 / cpu_khz)
22 *
23 * Then we use scaling math (suggested by george@mvista.com) to get:
24 * ns = cycles * (10^6 * SC / cpu_khz) / SC
25 * ns = cycles * cyc2ns_scale / SC
26 *
27 * And since SC is a constant power of two, we can convert the div
28 * into a shift.
29 *
Guillaume Chazarain53d517c2008-01-30 13:30:06 +010030 * We can use khz divisor instead of mhz to keep a better precision, since
Jeremy Fitzhardinge688340e2007-07-17 18:37:04 -070031 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
32 * (mathieu.desnoyers@polymtl.ca)
33 *
34 * -johnstul@us.ibm.com "math is hard, lets go shopping!"
Salman Qazi1f076482011-11-15 14:12:06 -080035 *
36 * In:
37 *
38 * ns = cycles * cyc2ns_scale / SC
39 *
40 * Although we may still have enough bits to store the value of ns,
41 * in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
42 * leading to an incorrect result.
43 *
44 * To avoid this, we can decompose 'cycles' into quotient and remainder
45 * of division by SC. Then,
46 *
47 * ns = (quot * SC + rem) * cyc2ns_scale / SC
48 * = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
49 *
50 * - sqazi@google.com
Jeremy Fitzhardinge688340e2007-07-17 18:37:04 -070051 */
Guillaume Chazarain53d517c2008-01-30 13:30:06 +010052
53DECLARE_PER_CPU(unsigned long, cyc2ns);
Peter Zijlstra84599f82009-06-16 12:34:17 -070054DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
Jeremy Fitzhardinge688340e2007-07-17 18:37:04 -070055
56#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
57
Guillaume Chazarain53d517c2008-01-30 13:30:06 +010058static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
Jeremy Fitzhardinge688340e2007-07-17 18:37:04 -070059{
Salman Qazi1f076482011-11-15 14:12:06 -080060 unsigned long long quot;
61 unsigned long long rem;
Peter Zijlstra84599f82009-06-16 12:34:17 -070062 int cpu = smp_processor_id();
63 unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
Salman Qazi1f076482011-11-15 14:12:06 -080064 quot = (cyc >> CYC2NS_SCALE_FACTOR);
65 rem = cyc & ((1ULL << CYC2NS_SCALE_FACTOR) - 1);
66 ns += quot * per_cpu(cyc2ns, cpu) +
67 ((rem * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR);
Peter Zijlstra84599f82009-06-16 12:34:17 -070068 return ns;
Jeremy Fitzhardinge688340e2007-07-17 18:37:04 -070069}
70
Guillaume Chazarain53d517c2008-01-30 13:30:06 +010071static inline unsigned long long cycles_2_ns(unsigned long long cyc)
72{
73 unsigned long long ns;
74 unsigned long flags;
75
76 local_irq_save(flags);
77 ns = __cycles_2_ns(cyc);
78 local_irq_restore(flags);
79
80 return ns;
81}
Jeremy Fitzhardinge688340e2007-07-17 18:37:04 -070082
H. Peter Anvin1965aae2008-10-22 22:26:29 -070083#endif /* _ASM_X86_TIMER_H */