2d42244ae7
In talking with Josip Loncaric, and his work on clock synchronization (see btime.sf.net), he mentioned that for really close synchronization, it is useful to have access to "hardware time", that is a notion of time that is not in any way adjusted by the clock slewing done to keep close time sync. Part of the issue is if we are using the kernel's ntp adjusted representation of time in order to measure how we should correct time, we can run into what Paul McKenney aptly described as "Painting a road using the lines we're painting as the guide". I had been thinking of a similar problem, and was trying to come up with a way to give users access to a purely hardware based time representation that avoided users having to know the underlying frequency and mask values needed to deal with the wide variety of possible underlying hardware counters. My solution is to introduce CLOCK_MONOTONIC_RAW. This exposes a nanosecond based time value, that increments starting at bootup and has no frequency adjustments made to it what so ever. The time is accessed from userspace via the posix_clock_gettime() syscall, passing CLOCK_MONOTONIC_RAW as the clock_id. Signed-off-by: John Stultz <johnstul@us.ibm.com> Signed-off-by: Roman Zippel <zippel@linux-m68k.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
245 lines
6.8 KiB
C
245 lines
6.8 KiB
C
/* linux/include/linux/clocksource.h
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*
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* This file contains the structure definitions for clocksources.
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*
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* If you are not a clocksource, or timekeeping code, you should
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* not be including this file!
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*/
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#ifndef _LINUX_CLOCKSOURCE_H
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#define _LINUX_CLOCKSOURCE_H
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#include <linux/types.h>
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#include <linux/timex.h>
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#include <linux/time.h>
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#include <linux/list.h>
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#include <linux/cache.h>
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#include <linux/timer.h>
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#include <asm/div64.h>
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#include <asm/io.h>
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/* clocksource cycle base type */
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typedef u64 cycle_t;
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struct clocksource;
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/**
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* struct clocksource - hardware abstraction for a free running counter
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* Provides mostly state-free accessors to the underlying hardware.
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*
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* @name: ptr to clocksource name
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* @list: list head for registration
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* @rating: rating value for selection (higher is better)
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* To avoid rating inflation the following
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* list should give you a guide as to how
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* to assign your clocksource a rating
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* 1-99: Unfit for real use
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* Only available for bootup and testing purposes.
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* 100-199: Base level usability.
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* Functional for real use, but not desired.
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* 200-299: Good.
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* A correct and usable clocksource.
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* 300-399: Desired.
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* A reasonably fast and accurate clocksource.
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* 400-499: Perfect
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* The ideal clocksource. A must-use where
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* available.
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* @read: returns a cycle value
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* @mask: bitmask for two's complement
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* subtraction of non 64 bit counters
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* @mult: cycle to nanosecond multiplier (adjusted by NTP)
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* @mult_orig: cycle to nanosecond multiplier (unadjusted by NTP)
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* @shift: cycle to nanosecond divisor (power of two)
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* @flags: flags describing special properties
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* @vread: vsyscall based read
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* @resume: resume function for the clocksource, if necessary
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* @cycle_interval: Used internally by timekeeping core, please ignore.
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* @xtime_interval: Used internally by timekeeping core, please ignore.
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*/
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struct clocksource {
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/*
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* First part of structure is read mostly
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*/
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char *name;
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struct list_head list;
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int rating;
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cycle_t (*read)(void);
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cycle_t mask;
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u32 mult;
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u32 mult_orig;
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u32 shift;
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unsigned long flags;
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cycle_t (*vread)(void);
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void (*resume)(void);
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#ifdef CONFIG_IA64
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void *fsys_mmio; /* used by fsyscall asm code */
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#define CLKSRC_FSYS_MMIO_SET(mmio, addr) ((mmio) = (addr))
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#else
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#define CLKSRC_FSYS_MMIO_SET(mmio, addr) do { } while (0)
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#endif
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/* timekeeping specific data, ignore */
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cycle_t cycle_interval;
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u64 xtime_interval;
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u32 raw_interval;
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/*
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* Second part is written at each timer interrupt
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* Keep it in a different cache line to dirty no
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* more than one cache line.
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*/
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cycle_t cycle_last ____cacheline_aligned_in_smp;
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u64 xtime_nsec;
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s64 error;
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struct timespec raw_time;
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#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
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/* Watchdog related data, used by the framework */
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struct list_head wd_list;
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cycle_t wd_last;
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#endif
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};
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extern struct clocksource *clock; /* current clocksource */
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/*
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* Clock source flags bits::
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*/
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#define CLOCK_SOURCE_IS_CONTINUOUS 0x01
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#define CLOCK_SOURCE_MUST_VERIFY 0x02
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#define CLOCK_SOURCE_WATCHDOG 0x10
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#define CLOCK_SOURCE_VALID_FOR_HRES 0x20
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/* simplify initialization of mask field */
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#define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
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/**
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* clocksource_khz2mult - calculates mult from khz and shift
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* @khz: Clocksource frequency in KHz
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* @shift_constant: Clocksource shift factor
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*
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* Helper functions that converts a khz counter frequency to a timsource
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* multiplier, given the clocksource shift value
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*/
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static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
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{
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/* khz = cyc/(Million ns)
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* mult/2^shift = ns/cyc
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* mult = ns/cyc * 2^shift
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* mult = 1Million/khz * 2^shift
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* mult = 1000000 * 2^shift / khz
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* mult = (1000000<<shift) / khz
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*/
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u64 tmp = ((u64)1000000) << shift_constant;
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tmp += khz/2; /* round for do_div */
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do_div(tmp, khz);
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return (u32)tmp;
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}
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/**
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* clocksource_hz2mult - calculates mult from hz and shift
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* @hz: Clocksource frequency in Hz
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* @shift_constant: Clocksource shift factor
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*
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* Helper functions that converts a hz counter
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* frequency to a timsource multiplier, given the
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* clocksource shift value
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*/
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static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
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{
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/* hz = cyc/(Billion ns)
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* mult/2^shift = ns/cyc
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* mult = ns/cyc * 2^shift
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* mult = 1Billion/hz * 2^shift
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* mult = 1000000000 * 2^shift / hz
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* mult = (1000000000<<shift) / hz
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*/
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u64 tmp = ((u64)1000000000) << shift_constant;
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tmp += hz/2; /* round for do_div */
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do_div(tmp, hz);
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return (u32)tmp;
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}
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/**
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* clocksource_read: - Access the clocksource's current cycle value
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* @cs: pointer to clocksource being read
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*
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* Uses the clocksource to return the current cycle_t value
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*/
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static inline cycle_t clocksource_read(struct clocksource *cs)
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{
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return cs->read();
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}
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/**
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* cyc2ns - converts clocksource cycles to nanoseconds
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* @cs: Pointer to clocksource
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* @cycles: Cycles
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*
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* Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
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*
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* XXX - This could use some mult_lxl_ll() asm optimization
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*/
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static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
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{
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u64 ret = (u64)cycles;
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ret = (ret * cs->mult) >> cs->shift;
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return ret;
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}
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/**
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* clocksource_calculate_interval - Calculates a clocksource interval struct
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*
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* @c: Pointer to clocksource.
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* @length_nsec: Desired interval length in nanoseconds.
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*
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* Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
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* pair and interval request.
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*
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* Unless you're the timekeeping code, you should not be using this!
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*/
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static inline void clocksource_calculate_interval(struct clocksource *c,
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unsigned long length_nsec)
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{
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u64 tmp;
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/* Do the ns -> cycle conversion first, using original mult */
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tmp = length_nsec;
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tmp <<= c->shift;
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tmp += c->mult_orig/2;
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do_div(tmp, c->mult_orig);
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c->cycle_interval = (cycle_t)tmp;
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if (c->cycle_interval == 0)
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c->cycle_interval = 1;
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/* Go back from cycles -> shifted ns, this time use ntp adjused mult */
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c->xtime_interval = (u64)c->cycle_interval * c->mult;
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c->raw_interval = ((u64)c->cycle_interval * c->mult_orig) >> c->shift;
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}
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/* used to install a new clocksource */
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extern int clocksource_register(struct clocksource*);
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extern void clocksource_unregister(struct clocksource*);
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extern void clocksource_touch_watchdog(void);
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extern struct clocksource* clocksource_get_next(void);
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extern void clocksource_change_rating(struct clocksource *cs, int rating);
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extern void clocksource_resume(void);
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#ifdef CONFIG_GENERIC_TIME_VSYSCALL
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extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
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extern void update_vsyscall_tz(void);
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#else
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static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
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{
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}
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static inline void update_vsyscall_tz(void)
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{
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}
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#endif
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#endif /* _LINUX_CLOCKSOURCE_H */
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