~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/kernel/time/jiffies.c

Version: ~ [ linux-5.4-rc7 ] ~ [ linux-5.3.11 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.84 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.154 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.201 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.201 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.77 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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>
 25 #include <linux/module.h>
 26 #include <linux/init.h>
 27 
 28 #include "timekeeping.h"
 29 
 30 
 31 /* Since jiffies uses a simple TICK_NSEC multiplier
 32  * conversion, the .shift value could be zero. However
 33  * this would make NTP adjustments impossible as they are
 34  * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
 35  * shift both the nominator and denominator the same
 36  * amount, and give ntp adjustments in units of 1/2^8
 37  *
 38  * The value 8 is somewhat carefully chosen, as anything
 39  * larger can result in overflows. TICK_NSEC grows as HZ
 40  * shrinks, so values greater than 8 overflow 32bits when
 41  * HZ=100.
 42  */
 43 #if HZ < 34
 44 #define JIFFIES_SHIFT   6
 45 #elif HZ < 67
 46 #define JIFFIES_SHIFT   7
 47 #else
 48 #define JIFFIES_SHIFT   8
 49 #endif
 50 
 51 static u64 jiffies_read(struct clocksource *cs)
 52 {
 53         return (u64) jiffies;
 54 }
 55 
 56 /*
 57  * The Jiffies based clocksource is the lowest common
 58  * denominator clock source which should function on
 59  * all systems. It has the same coarse resolution as
 60  * the timer interrupt frequency HZ and it suffers
 61  * inaccuracies caused by missed or lost timer
 62  * interrupts and the inability for the timer
 63  * interrupt hardware to accuratly tick at the
 64  * requested HZ value. It is also not recommended
 65  * for "tick-less" systems.
 66  */
 67 static struct clocksource clocksource_jiffies = {
 68         .name           = "jiffies",
 69         .rating         = 1, /* lowest valid rating*/
 70         .read           = jiffies_read,
 71         .mask           = CLOCKSOURCE_MASK(32),
 72         .mult           = TICK_NSEC << JIFFIES_SHIFT, /* details above */
 73         .shift          = JIFFIES_SHIFT,
 74         .max_cycles     = 10,
 75 };
 76 
 77 __cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
 78 
 79 #if (BITS_PER_LONG < 64)
 80 u64 get_jiffies_64(void)
 81 {
 82         unsigned long seq;
 83         u64 ret;
 84 
 85         do {
 86                 seq = read_seqbegin(&jiffies_lock);
 87                 ret = jiffies_64;
 88         } while (read_seqretry(&jiffies_lock, seq));
 89         return ret;
 90 }
 91 EXPORT_SYMBOL(get_jiffies_64);
 92 #endif
 93 
 94 EXPORT_SYMBOL(jiffies);
 95 
 96 static int __init init_jiffies_clocksource(void)
 97 {
 98         return __clocksource_register(&clocksource_jiffies);
 99 }
100 
101 core_initcall(init_jiffies_clocksource);
102 
103 struct clocksource * __init __weak clocksource_default_clock(void)
104 {
105         return &clocksource_jiffies;
106 }
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 
134         __clocksource_register(&refined_jiffies);
135         return 0;
136 }
137 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp