Commit | Line | Data |
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734efb46 | 1 | /*********************************************************************** |
2 | * linux/kernel/time/jiffies.c | |
3 | * | |
4 | * This file contains the jiffies based clocksource. | |
5 | * | |
6 | * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com) | |
7 | * | |
8 | * This program is free software; you can redistribute it and/or modify | |
9 | * it under the terms of the GNU General Public License as published by | |
10 | * the Free Software Foundation; either version 2 of the License, or | |
11 | * (at your option) any later version. | |
12 | * | |
13 | * This program is distributed in the hope that it will be useful, | |
14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
16 | * GNU General Public License for more details. | |
17 | * | |
18 | * You should have received a copy of the GNU General Public License | |
19 | * along with this program; if not, write to the Free Software | |
20 | * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
21 | * | |
22 | ************************************************************************/ | |
23 | #include <linux/clocksource.h> | |
24 | #include <linux/jiffies.h> | |
fbad1ea9 | 25 | #include <linux/module.h> |
734efb46 | 26 | #include <linux/init.h> |
27 | ||
bfb83b27 | 28 | #include "timekeeping.h" |
e2830b5c | 29 | |
734efb46 | 30 | /* The Jiffies based clocksource is the lowest common |
31 | * denominator clock source which should function on | |
32 | * all systems. It has the same coarse resolution as | |
33 | * the timer interrupt frequency HZ and it suffers | |
34 | * inaccuracies caused by missed or lost timer | |
35 | * interrupts and the inability for the timer | |
36 | * interrupt hardware to accuratly tick at the | |
25985edc | 37 | * requested HZ value. It is also not recommended |
734efb46 | 38 | * for "tick-less" systems. |
39 | */ | |
b3c869d3 | 40 | #define NSEC_PER_JIFFY ((NSEC_PER_SEC+HZ/2)/HZ) |
734efb46 | 41 | |
42 | /* Since jiffies uses a simple NSEC_PER_JIFFY multiplier | |
43 | * conversion, the .shift value could be zero. However | |
44 | * this would make NTP adjustments impossible as they are | |
45 | * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to | |
46 | * shift both the nominator and denominator the same | |
47 | * amount, and give ntp adjustments in units of 1/2^8 | |
48 | * | |
49 | * The value 8 is somewhat carefully chosen, as anything | |
50 | * larger can result in overflows. NSEC_PER_JIFFY grows as | |
025dfdaf | 51 | * HZ shrinks, so values greater than 8 overflow 32bits when |
734efb46 | 52 | * HZ=100. |
53 | */ | |
80d767d7 MP |
54 | #if HZ < 34 |
55 | #define JIFFIES_SHIFT 6 | |
56 | #elif HZ < 67 | |
57 | #define JIFFIES_SHIFT 7 | |
58 | #else | |
734efb46 | 59 | #define JIFFIES_SHIFT 8 |
80d767d7 | 60 | #endif |
734efb46 | 61 | |
8e19608e | 62 | static cycle_t jiffies_read(struct clocksource *cs) |
734efb46 | 63 | { |
64 | return (cycle_t) jiffies; | |
65 | } | |
66 | ||
f95a9857 | 67 | static struct clocksource clocksource_jiffies = { |
734efb46 | 68 | .name = "jiffies", |
3f4a0b91 | 69 | .rating = 1, /* lowest valid rating*/ |
734efb46 | 70 | .read = jiffies_read, |
232d2637 | 71 | .mask = CLOCKSOURCE_MASK(32), |
734efb46 | 72 | .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ |
73 | .shift = JIFFIES_SHIFT, | |
3c17ad19 | 74 | .max_cycles = 10, |
734efb46 | 75 | }; |
76 | ||
d6ad4187 JS |
77 | __cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock); |
78 | ||
fbad1ea9 TH |
79 | #if (BITS_PER_LONG < 64) |
80 | u64 get_jiffies_64(void) | |
81 | { | |
82 | unsigned long seq; | |
83 | u64 ret; | |
84 | ||
85 | do { | |
d6ad4187 | 86 | seq = read_seqbegin(&jiffies_lock); |
fbad1ea9 | 87 | ret = jiffies_64; |
d6ad4187 | 88 | } while (read_seqretry(&jiffies_lock, seq)); |
fbad1ea9 TH |
89 | return ret; |
90 | } | |
91 | EXPORT_SYMBOL(get_jiffies_64); | |
92 | #endif | |
93 | ||
94 | EXPORT_SYMBOL(jiffies); | |
95 | ||
734efb46 | 96 | static int __init init_jiffies_clocksource(void) |
97 | { | |
f8935983 | 98 | return __clocksource_register(&clocksource_jiffies); |
734efb46 | 99 | } |
100 | ||
98de9e3b | 101 | core_initcall(init_jiffies_clocksource); |
f1b82746 MS |
102 | |
103 | struct clocksource * __init __weak clocksource_default_clock(void) | |
104 | { | |
105 | return &clocksource_jiffies; | |
106 | } | |
b3c869d3 JS |
107 | |
108 | struct clocksource refined_jiffies; | |
109 | ||
110 | int register_refined_jiffies(long cycles_per_second) | |
111 | { | |
112 | u64 nsec_per_tick, shift_hz; | |
113 | long cycles_per_tick; | |
114 | ||
115 | ||
116 | ||
117 | refined_jiffies = clocksource_jiffies; | |
118 | refined_jiffies.name = "refined-jiffies"; | |
119 | refined_jiffies.rating++; | |
120 | ||
121 | /* Calc cycles per tick */ | |
122 | cycles_per_tick = (cycles_per_second + HZ/2)/HZ; | |
123 | /* shift_hz stores hz<<8 for extra accuracy */ | |
124 | shift_hz = (u64)cycles_per_second << 8; | |
125 | shift_hz += cycles_per_tick/2; | |
126 | do_div(shift_hz, cycles_per_tick); | |
127 | /* Calculate nsec_per_tick using shift_hz */ | |
128 | nsec_per_tick = (u64)NSEC_PER_SEC << 8; | |
129 | nsec_per_tick += (u32)shift_hz/2; | |
130 | do_div(nsec_per_tick, (u32)shift_hz); | |
131 | ||
132 | refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT; | |
133 | ||
f8935983 | 134 | __clocksource_register(&refined_jiffies); |
b3c869d3 JS |
135 | return 0; |
136 | } |