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Access to time requires to touch two cachelines at minimum 1) The timekeeper data structure 2) The clocksource data structure The access to the clocksource data structure can be avoided as almost all clocksource implementations ignore the argument to the read callback, which is a pointer to the clocksource. But the core needs to touch it to access the members @read and @mask. So we are better off by copying the @read function pointer and the @mask from the clocksource to the core data structure itself. For the most used ktime_get() access all required data including the @read and @mask copies fits together with the sequence counter into a single 64 byte cacheline. For the other time access functions we touch in the current code three cache lines in the worst case. But with the clocksource data copies we can reduce that to two adjacent cachelines, which is more efficient than disjunct cache lines. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>
112 lines
3 KiB
C
112 lines
3 KiB
C
/*
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* You SHOULD NOT be including this unless you're vsyscall
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* handling code or timekeeping internal code!
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*/
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#ifndef _LINUX_TIMEKEEPER_INTERNAL_H
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#define _LINUX_TIMEKEEPER_INTERNAL_H
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#include <linux/clocksource.h>
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#include <linux/jiffies.h>
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#include <linux/time.h>
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/*
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* Structure holding internal timekeeping values.
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*
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* Note: wall_to_monotonic is what we need to add to xtime (or xtime
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* corrected for sub jiffie times) to get to monotonic time.
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* Monotonic is pegged at zero at system boot time, so
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* wall_to_monotonic will be negative, however, we will ALWAYS keep
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* the tv_nsec part positive so we can use the usual normalization.
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*
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* wall_to_monotonic is moved after resume from suspend for the
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* monotonic time not to jump. To calculate the real boot time offset
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* we need to do offs_real - offs_boot.
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*
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* - wall_to_monotonic is no longer the boot time, getboottime must be
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* used instead.
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*/
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struct timekeeper {
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/* Current clocksource used for timekeeping. */
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struct clocksource *clock;
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/* Read function of @clock */
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cycle_t (*read)(struct clocksource *cs);
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/* Bitmask for two's complement subtraction of non 64bit counters */
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cycle_t mask;
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/* Last cycle value */
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cycle_t cycle_last;
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/* NTP adjusted clock multiplier */
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u32 mult;
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/* The shift value of the current clocksource. */
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u32 shift;
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/* Clock shifted nano seconds */
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u64 xtime_nsec;
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/* Monotonic base time */
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ktime_t base_mono;
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/* Current CLOCK_REALTIME time in seconds */
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u64 xtime_sec;
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/* CLOCK_REALTIME to CLOCK_MONOTONIC offset */
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struct timespec64 wall_to_monotonic;
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/* Offset clock monotonic -> clock realtime */
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ktime_t offs_real;
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/* Offset clock monotonic -> clock boottime */
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ktime_t offs_boot;
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/* Offset clock monotonic -> clock tai */
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ktime_t offs_tai;
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/* The current UTC to TAI offset in seconds */
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s32 tai_offset;
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/* Monotonic raw base time */
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ktime_t base_raw;
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/* The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock. */
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struct timespec64 raw_time;
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/* Number of clock cycles in one NTP interval. */
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cycle_t cycle_interval;
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/* Number of clock shifted nano seconds in one NTP interval. */
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u64 xtime_interval;
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/* shifted nano seconds left over when rounding cycle_interval */
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s64 xtime_remainder;
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/* Raw nano seconds accumulated per NTP interval. */
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u32 raw_interval;
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/*
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* Difference between accumulated time and NTP time in ntp
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* shifted nano seconds.
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*/
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s64 ntp_error;
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/*
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* Shift conversion between clock shifted nano seconds and
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* ntp shifted nano seconds.
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*/
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u32 ntp_error_shift;
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};
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#ifdef CONFIG_GENERIC_TIME_VSYSCALL
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extern void update_vsyscall(struct timekeeper *tk);
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extern void update_vsyscall_tz(void);
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#elif defined(CONFIG_GENERIC_TIME_VSYSCALL_OLD)
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extern void update_vsyscall_old(struct timespec *ts, struct timespec *wtm,
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struct clocksource *c, u32 mult,
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cycles_t cycle_last);
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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 timekeeper *tk)
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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_TIMEKEEPER_INTERNAL_H */
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