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ea7dfc423c
commit 80d767d770fd9c697e434fd080c2db7b5c60c6dd upstream. When compiling for the IA-64 ski emulator, HZ is set to 32 because the emulation is slow and we don't want to waste too many cycles processing timers. Alpha also has an option to set HZ to 32. This causes integer underflow in kernel/time/jiffies.c: kernel/time/jiffies.c:66:2: warning: large integer implicitly truncated to unsigned type [-Woverflow] .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ ^ This patch reduces the JIFFIES_SHIFT value to avoid the overflow. Signed-off-by: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz> Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1401241639100.23871@file01.intranet.prod.int.rdu2.redhat.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
135 lines
3.9 KiB
C
135 lines
3.9 KiB
C
/***********************************************************************
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* linux/kernel/time/jiffies.c
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*
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* This file contains the jiffies based clocksource.
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*
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* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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************************************************************************/
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#include <linux/clocksource.h>
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#include <linux/jiffies.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include "tick-internal.h"
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/* The Jiffies based clocksource is the lowest common
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* denominator clock source which should function on
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* all systems. It has the same coarse resolution as
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* the timer interrupt frequency HZ and it suffers
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* inaccuracies caused by missed or lost timer
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* interrupts and the inability for the timer
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* interrupt hardware to accuratly tick at the
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* requested HZ value. It is also not recommended
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* for "tick-less" systems.
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*/
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#define NSEC_PER_JIFFY ((NSEC_PER_SEC+HZ/2)/HZ)
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/* Since jiffies uses a simple NSEC_PER_JIFFY multiplier
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* conversion, the .shift value could be zero. However
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* this would make NTP adjustments impossible as they are
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* in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
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* shift both the nominator and denominator the same
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* amount, and give ntp adjustments in units of 1/2^8
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*
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* The value 8 is somewhat carefully chosen, as anything
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* larger can result in overflows. NSEC_PER_JIFFY grows as
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* HZ shrinks, so values greater than 8 overflow 32bits when
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* HZ=100.
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*/
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#if HZ < 34
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#define JIFFIES_SHIFT 6
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#elif HZ < 67
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#define JIFFIES_SHIFT 7
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#else
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#define JIFFIES_SHIFT 8
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#endif
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static cycle_t jiffies_read(struct clocksource *cs)
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{
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return (cycle_t) jiffies;
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}
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static struct clocksource clocksource_jiffies = {
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.name = "jiffies",
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.rating = 1, /* lowest valid rating*/
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.read = jiffies_read,
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.mask = 0xffffffff, /*32bits*/
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.mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
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.shift = JIFFIES_SHIFT,
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};
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__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
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#if (BITS_PER_LONG < 64)
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u64 get_jiffies_64(void)
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{
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unsigned long seq;
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u64 ret;
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do {
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seq = read_seqbegin(&jiffies_lock);
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ret = jiffies_64;
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} while (read_seqretry(&jiffies_lock, seq));
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return ret;
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}
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EXPORT_SYMBOL(get_jiffies_64);
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#endif
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EXPORT_SYMBOL(jiffies);
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static int __init init_jiffies_clocksource(void)
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{
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return clocksource_register(&clocksource_jiffies);
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}
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core_initcall(init_jiffies_clocksource);
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struct clocksource * __init __weak clocksource_default_clock(void)
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{
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return &clocksource_jiffies;
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}
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struct clocksource refined_jiffies;
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int register_refined_jiffies(long cycles_per_second)
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{
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u64 nsec_per_tick, shift_hz;
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long cycles_per_tick;
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refined_jiffies = clocksource_jiffies;
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refined_jiffies.name = "refined-jiffies";
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refined_jiffies.rating++;
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/* Calc cycles per tick */
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cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
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/* shift_hz stores hz<<8 for extra accuracy */
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shift_hz = (u64)cycles_per_second << 8;
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shift_hz += cycles_per_tick/2;
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do_div(shift_hz, cycles_per_tick);
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/* Calculate nsec_per_tick using shift_hz */
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nsec_per_tick = (u64)NSEC_PER_SEC << 8;
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nsec_per_tick += (u32)shift_hz/2;
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do_div(nsec_per_tick, (u32)shift_hz);
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refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
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clocksource_register(&refined_jiffies);
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return 0;
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}
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