/*********************************************************************** * This file contains the jiffies based clocksource. * * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com) * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. * ************************************************************************/ #include #include #include #include #include "timekeeping.h" /* Since jiffies uses a simple TICK_NSEC multiplier * conversion, the .shift value could be zero. However * this would make NTP adjustments impossible as they are * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to * shift both the nominator and denominator the same * amount, and give ntp adjustments in units of 1/2^8 * * The value 8 is somewhat carefully chosen, as anything * larger can result in overflows. TICK_NSEC grows as HZ * shrinks, so values greater than 8 overflow 32bits when * HZ=100. */ #if HZ < 34 #define JIFFIES_SHIFT 6 #elif HZ < 67 #define JIFFIES_SHIFT 7 #else #define JIFFIES_SHIFT 8 #endif static u64 jiffies_read(struct clocksource *cs) { return (u64) jiffies; } /* * The Jiffies based clocksource is the lowest common * denominator clock source which should function on * all systems. It has the same coarse resolution as * the timer interrupt frequency HZ and it suffers * inaccuracies caused by missed or lost timer * interrupts and the inability for the timer * interrupt hardware to accuratly tick at the * requested HZ value. It is also not recommended * for "tick-less" systems. */ static struct clocksource clocksource_jiffies = { .name = "jiffies", .rating = 1, /* lowest valid rating*/ .read = jiffies_read, .mask = CLOCKSOURCE_MASK(32), .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */ .shift = JIFFIES_SHIFT, .max_cycles = 10, }; __cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock); #if (BITS_PER_LONG < 64) u64 get_jiffies_64(void) { unsigned long seq; u64 ret; do { seq = read_seqbegin(&jiffies_lock); ret = jiffies_64; } while (read_seqretry(&jiffies_lock, seq)); return ret; } EXPORT_SYMBOL(get_jiffies_64); #endif EXPORT_SYMBOL(jiffies); static int __init init_jiffies_clocksource(void) { return __clocksource_register(&clocksource_jiffies); } core_initcall(init_jiffies_clocksource); struct clocksource * __init __weak clocksource_default_clock(void) { return &clocksource_jiffies; } struct clocksource refined_jiffies; int register_refined_jiffies(long cycles_per_second) { u64 nsec_per_tick, shift_hz; long cycles_per_tick; refined_jiffies = clocksource_jiffies; refined_jiffies.name = "refined-jiffies"; refined_jiffies.rating++; /* Calc cycles per tick */ cycles_per_tick = (cycles_per_second + HZ/2)/HZ; /* shift_hz stores hz<<8 for extra accuracy */ shift_hz = (u64)cycles_per_second << 8; shift_hz += cycles_per_tick/2; do_div(shift_hz, cycles_per_tick); /* Calculate nsec_per_tick using shift_hz */ nsec_per_tick = (u64)NSEC_PER_SEC << 8; nsec_per_tick += (u32)shift_hz/2; do_div(nsec_per_tick, (u32)shift_hz); refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT; __clocksource_register(&refined_jiffies); return 0; }