1734efb46Sjohn stultz /*********************************************************************** 2734efb46Sjohn stultz * linux/kernel/time/jiffies.c 3734efb46Sjohn stultz * 4734efb46Sjohn stultz * This file contains the jiffies based clocksource. 5734efb46Sjohn stultz * 6734efb46Sjohn stultz * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com) 7734efb46Sjohn stultz * 8734efb46Sjohn stultz * This program is free software; you can redistribute it and/or modify 9734efb46Sjohn stultz * it under the terms of the GNU General Public License as published by 10734efb46Sjohn stultz * the Free Software Foundation; either version 2 of the License, or 11734efb46Sjohn stultz * (at your option) any later version. 12734efb46Sjohn stultz * 13734efb46Sjohn stultz * This program is distributed in the hope that it will be useful, 14734efb46Sjohn stultz * but WITHOUT ANY WARRANTY; without even the implied warranty of 15734efb46Sjohn stultz * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 16734efb46Sjohn stultz * GNU General Public License for more details. 17734efb46Sjohn stultz * 18734efb46Sjohn stultz * You should have received a copy of the GNU General Public License 19734efb46Sjohn stultz * along with this program; if not, write to the Free Software 20734efb46Sjohn stultz * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 21734efb46Sjohn stultz * 22734efb46Sjohn stultz ************************************************************************/ 23734efb46Sjohn stultz #include <linux/clocksource.h> 24734efb46Sjohn stultz #include <linux/jiffies.h> 25fbad1ea9STorben Hohn #include <linux/module.h> 26734efb46Sjohn stultz #include <linux/init.h> 27734efb46Sjohn stultz 28e2830b5cSTorben Hohn #include "tick-internal.h" 29e2830b5cSTorben Hohn 30734efb46Sjohn stultz /* The Jiffies based clocksource is the lowest common 31734efb46Sjohn stultz * denominator clock source which should function on 32734efb46Sjohn stultz * all systems. It has the same coarse resolution as 33734efb46Sjohn stultz * the timer interrupt frequency HZ and it suffers 34734efb46Sjohn stultz * inaccuracies caused by missed or lost timer 35734efb46Sjohn stultz * interrupts and the inability for the timer 36734efb46Sjohn stultz * interrupt hardware to accuratly tick at the 3725985edcSLucas De Marchi * requested HZ value. It is also not recommended 38734efb46Sjohn stultz * for "tick-less" systems. 39734efb46Sjohn stultz */ 40b3c869d3SJohn Stultz #define NSEC_PER_JIFFY ((NSEC_PER_SEC+HZ/2)/HZ) 41734efb46Sjohn stultz 42734efb46Sjohn stultz /* Since jiffies uses a simple NSEC_PER_JIFFY multiplier 43734efb46Sjohn stultz * conversion, the .shift value could be zero. However 44734efb46Sjohn stultz * this would make NTP adjustments impossible as they are 45734efb46Sjohn stultz * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to 46734efb46Sjohn stultz * shift both the nominator and denominator the same 47734efb46Sjohn stultz * amount, and give ntp adjustments in units of 1/2^8 48734efb46Sjohn stultz * 49734efb46Sjohn stultz * The value 8 is somewhat carefully chosen, as anything 50734efb46Sjohn stultz * larger can result in overflows. NSEC_PER_JIFFY grows as 51025dfdafSFrederik Schwarzer * HZ shrinks, so values greater than 8 overflow 32bits when 52734efb46Sjohn stultz * HZ=100. 53734efb46Sjohn stultz */ 54734efb46Sjohn stultz #define JIFFIES_SHIFT 8 55734efb46Sjohn stultz 568e19608eSMagnus Damm static cycle_t jiffies_read(struct clocksource *cs) 57734efb46Sjohn stultz { 58734efb46Sjohn stultz return (cycle_t) jiffies; 59734efb46Sjohn stultz } 60734efb46Sjohn stultz 61f95a9857SLars-Peter Clausen static struct clocksource clocksource_jiffies = { 62734efb46Sjohn stultz .name = "jiffies", 633f4a0b91Sjohn stultz .rating = 1, /* lowest valid rating*/ 64734efb46Sjohn stultz .read = jiffies_read, 65734efb46Sjohn stultz .mask = 0xffffffff, /*32bits*/ 66734efb46Sjohn stultz .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ 67734efb46Sjohn stultz .shift = JIFFIES_SHIFT, 68734efb46Sjohn stultz }; 69734efb46Sjohn stultz 70*d6ad4187SJohn Stultz __cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock); 71*d6ad4187SJohn Stultz 72fbad1ea9STorben Hohn #if (BITS_PER_LONG < 64) 73fbad1ea9STorben Hohn u64 get_jiffies_64(void) 74fbad1ea9STorben Hohn { 75fbad1ea9STorben Hohn unsigned long seq; 76fbad1ea9STorben Hohn u64 ret; 77fbad1ea9STorben Hohn 78fbad1ea9STorben Hohn do { 79*d6ad4187SJohn Stultz seq = read_seqbegin(&jiffies_lock); 80fbad1ea9STorben Hohn ret = jiffies_64; 81*d6ad4187SJohn Stultz } while (read_seqretry(&jiffies_lock, seq)); 82fbad1ea9STorben Hohn return ret; 83fbad1ea9STorben Hohn } 84fbad1ea9STorben Hohn EXPORT_SYMBOL(get_jiffies_64); 85fbad1ea9STorben Hohn #endif 86fbad1ea9STorben Hohn 87fbad1ea9STorben Hohn EXPORT_SYMBOL(jiffies); 88fbad1ea9STorben Hohn 89734efb46Sjohn stultz static int __init init_jiffies_clocksource(void) 90734efb46Sjohn stultz { 91a2752549Sjohn stultz return clocksource_register(&clocksource_jiffies); 92734efb46Sjohn stultz } 93734efb46Sjohn stultz 9498de9e3bSjohn stultz core_initcall(init_jiffies_clocksource); 95f1b82746SMartin Schwidefsky 96f1b82746SMartin Schwidefsky struct clocksource * __init __weak clocksource_default_clock(void) 97f1b82746SMartin Schwidefsky { 98f1b82746SMartin Schwidefsky return &clocksource_jiffies; 99f1b82746SMartin Schwidefsky } 100b3c869d3SJohn Stultz 101b3c869d3SJohn Stultz struct clocksource refined_jiffies; 102b3c869d3SJohn Stultz 103b3c869d3SJohn Stultz int register_refined_jiffies(long cycles_per_second) 104b3c869d3SJohn Stultz { 105b3c869d3SJohn Stultz u64 nsec_per_tick, shift_hz; 106b3c869d3SJohn Stultz long cycles_per_tick; 107b3c869d3SJohn Stultz 108b3c869d3SJohn Stultz 109b3c869d3SJohn Stultz 110b3c869d3SJohn Stultz refined_jiffies = clocksource_jiffies; 111b3c869d3SJohn Stultz refined_jiffies.name = "refined-jiffies"; 112b3c869d3SJohn Stultz refined_jiffies.rating++; 113b3c869d3SJohn Stultz 114b3c869d3SJohn Stultz /* Calc cycles per tick */ 115b3c869d3SJohn Stultz cycles_per_tick = (cycles_per_second + HZ/2)/HZ; 116b3c869d3SJohn Stultz /* shift_hz stores hz<<8 for extra accuracy */ 117b3c869d3SJohn Stultz shift_hz = (u64)cycles_per_second << 8; 118b3c869d3SJohn Stultz shift_hz += cycles_per_tick/2; 119b3c869d3SJohn Stultz do_div(shift_hz, cycles_per_tick); 120b3c869d3SJohn Stultz /* Calculate nsec_per_tick using shift_hz */ 121b3c869d3SJohn Stultz nsec_per_tick = (u64)NSEC_PER_SEC << 8; 122b3c869d3SJohn Stultz nsec_per_tick += (u32)shift_hz/2; 123b3c869d3SJohn Stultz do_div(nsec_per_tick, (u32)shift_hz); 124b3c869d3SJohn Stultz 125b3c869d3SJohn Stultz refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT; 126b3c869d3SJohn Stultz 127b3c869d3SJohn Stultz clocksource_register(&refined_jiffies); 128b3c869d3SJohn Stultz return 0; 129b3c869d3SJohn Stultz } 130