diff options
Diffstat (limited to 'include/linux/timekeeper_internal.h')
| -rw-r--r-- | include/linux/timekeeper_internal.h | 114 |
1 files changed, 61 insertions, 53 deletions
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h index 902c20ef495a..e39d4d563b19 100644 --- a/include/linux/timekeeper_internal.h +++ b/include/linux/timekeeper_internal.h @@ -26,7 +26,7 @@ * occupies a single 64byte cache line. * * The struct is separate from struct timekeeper as it is also used - * for a fast NMI safe accessors. + * for the fast NMI safe accessors. * * @base_real is for the fast NMI safe accessor to allow reading clock * realtime from any context. @@ -44,33 +44,38 @@ struct tk_read_base { /** * struct timekeeper - Structure holding internal timekeeping values. - * @tkr_mono: The readout base structure for CLOCK_MONOTONIC - * @tkr_raw: The readout base structure for CLOCK_MONOTONIC_RAW - * @xtime_sec: Current CLOCK_REALTIME time in seconds - * @ktime_sec: Current CLOCK_MONOTONIC time in seconds - * @wall_to_monotonic: CLOCK_REALTIME to CLOCK_MONOTONIC offset - * @offs_real: Offset clock monotonic -> clock realtime - * @offs_boot: Offset clock monotonic -> clock boottime - * @offs_tai: Offset clock monotonic -> clock tai - * @tai_offset: The current UTC to TAI offset in seconds - * @clock_was_set_seq: The sequence number of clock was set events - * @cs_was_changed_seq: The sequence number of clocksource change events - * @next_leap_ktime: CLOCK_MONOTONIC time value of a pending leap-second - * @raw_sec: CLOCK_MONOTONIC_RAW time in seconds - * @monotonic_to_boot: CLOCK_MONOTONIC to CLOCK_BOOTTIME offset - * @cycle_interval: Number of clock cycles in one NTP interval - * @xtime_interval: Number of clock shifted nano seconds in one NTP - * interval. - * @xtime_remainder: Shifted nano seconds left over when rounding - * @cycle_interval - * @raw_interval: Shifted raw nano seconds accumulated per NTP interval. - * @ntp_error: Difference between accumulated time and NTP time in ntp - * shifted nano seconds. - * @ntp_error_shift: Shift conversion between clock shifted nano seconds and - * ntp shifted nano seconds. - * @last_warning: Warning ratelimiter (DEBUG_TIMEKEEPING) - * @underflow_seen: Underflow warning flag (DEBUG_TIMEKEEPING) - * @overflow_seen: Overflow warning flag (DEBUG_TIMEKEEPING) + * @tkr_mono: The readout base structure for CLOCK_MONOTONIC + * @xtime_sec: Current CLOCK_REALTIME time in seconds + * @ktime_sec: Current CLOCK_MONOTONIC time in seconds + * @wall_to_monotonic: CLOCK_REALTIME to CLOCK_MONOTONIC offset + * @offs_real: Offset clock monotonic -> clock realtime + * @offs_boot: Offset clock monotonic -> clock boottime + * @offs_tai: Offset clock monotonic -> clock tai + * @tai_offset: The current UTC to TAI offset in seconds + * @tkr_raw: The readout base structure for CLOCK_MONOTONIC_RAW + * @raw_sec: CLOCK_MONOTONIC_RAW time in seconds + * @clock_was_set_seq: The sequence number of clock was set events + * @cs_was_changed_seq: The sequence number of clocksource change events + * @monotonic_to_boot: CLOCK_MONOTONIC to CLOCK_BOOTTIME offset + * @cycle_interval: Number of clock cycles in one NTP interval + * @xtime_interval: Number of clock shifted nano seconds in one NTP + * interval. + * @xtime_remainder: Shifted nano seconds left over when rounding + * @cycle_interval + * @raw_interval: Shifted raw nano seconds accumulated per NTP interval. + * @next_leap_ktime: CLOCK_MONOTONIC time value of a pending leap-second + * @ntp_tick: The ntp_tick_length() value currently being + * used. This cached copy ensures we consistently + * apply the tick length for an entire tick, as + * ntp_tick_length may change mid-tick, and we don't + * want to apply that new value to the tick in + * progress. + * @ntp_error: Difference between accumulated time and NTP time in ntp + * shifted nano seconds. + * @ntp_error_shift: Shift conversion between clock shifted nano seconds and + * ntp shifted nano seconds. + * @ntp_err_mult: Multiplication factor for scaled math conversion + * @skip_second_overflow: Flag used to avoid updating NTP twice with same second * * Note: For timespec(64) based interfaces wall_to_monotonic is what * we need to add to xtime (or xtime corrected for sub jiffy times) @@ -88,10 +93,28 @@ struct tk_read_base { * * @monotonic_to_boottime is a timespec64 representation of @offs_boot to * accelerate the VDSO update for CLOCK_BOOTTIME. + * + * The cacheline ordering of the structure is optimized for in kernel usage of + * the ktime_get() and ktime_get_ts64() family of time accessors. Struct + * timekeeper is prepended in the core timekeeping code with a sequence count, + * which results in the following cacheline layout: + * + * 0: seqcount, tkr_mono + * 1: xtime_sec ... tai_offset + * 2: tkr_raw, raw_sec + * 3,4: Internal variables + * + * Cacheline 0,1 contain the data which is used for accessing + * CLOCK_MONOTONIC/REALTIME/BOOTTIME/TAI, while cacheline 2 contains the + * data for accessing CLOCK_MONOTONIC_RAW. Cacheline 3,4 are internal + * variables which are only accessed during timekeeper updates once per + * tick. */ struct timekeeper { + /* Cacheline 0 (together with prepended seqcount of timekeeper core): */ struct tk_read_base tkr_mono; - struct tk_read_base tkr_raw; + + /* Cacheline 1: */ u64 xtime_sec; unsigned long ktime_sec; struct timespec64 wall_to_monotonic; @@ -99,43 +122,28 @@ struct timekeeper { ktime_t offs_boot; ktime_t offs_tai; s32 tai_offset; + + /* Cacheline 2: */ + struct tk_read_base tkr_raw; + u64 raw_sec; + + /* Cachline 3 and 4 (timekeeping internal variables): */ unsigned int clock_was_set_seq; u8 cs_was_changed_seq; - ktime_t next_leap_ktime; - u64 raw_sec; + struct timespec64 monotonic_to_boot; - /* The following members are for timekeeping internal use */ u64 cycle_interval; u64 xtime_interval; s64 xtime_remainder; u64 raw_interval; - /* The ntp_tick_length() value currently being used. - * This cached copy ensures we consistently apply the tick - * length for an entire tick, as ntp_tick_length may change - * mid-tick, and we don't want to apply that new value to - * the tick in progress. - */ + + ktime_t next_leap_ktime; u64 ntp_tick; - /* Difference between accumulated time and NTP time in ntp - * shifted nano seconds. */ s64 ntp_error; u32 ntp_error_shift; u32 ntp_err_mult; - /* Flag used to avoid updating NTP twice with same second */ u32 skip_second_overflow; -#ifdef CONFIG_DEBUG_TIMEKEEPING - long last_warning; - /* - * These simple flag variables are managed - * without locks, which is racy, but they are - * ok since we don't really care about being - * super precise about how many events were - * seen, just that a problem was observed. - */ - int underflow_seen; - int overflow_seen; -#endif }; #ifdef CONFIG_GENERIC_TIME_VSYSCALL |