• Kevin Brodsky's avatar
    arm64: Add support for CLOCK_MONOTONIC_RAW in clock_gettime() vDSO · 49eea433
    Kevin Brodsky authored
    So far the arm64 clock_gettime() vDSO implementation only supported
    the following clocks, falling back to the syscall for the others:
    - CLOCK_REALTIME{,_COARSE}
    - CLOCK_MONOTONIC{,_COARSE}
    
    This patch adds support for the CLOCK_MONOTONIC_RAW clock, taking
    advantage of the recent refactoring of the vDSO time functions. Like
    the non-_COARSE clocks, this only works when the "arch_sys_counter"
    clocksource is in use (allowing us to read the current time from the
    virtual counter register), otherwise we also have to fall back to the
    syscall.
    
    Most of the data is shared with CLOCK_MONOTONIC, and the algorithm is
    similar. The reference implementation in kernel/time/timekeeping.c
    shows that:
    - CLOCK_MONOTONIC = tk->wall_to_monotonic + tk->xtime_sec +
      timekeeping_get_ns(&tk->tkr_mono)
    - CLOCK_MONOTONIC_RAW = tk->raw_time + timekeeping_get_ns(&tk->tkr_raw)
    - tkr_mono and tkr_raw are identical (in particular, same
      clocksource), except these members:
      * mult (only mono's multiplier is NTP-adjusted)
      * xtime_nsec (always 0 for raw)
    
    Therefore, tk->raw_time and tkr_raw->mult are now also stored in the
    vDSO data page.
    
    Cc: Ali Saidi <ali.saidi@arm.com>
    Signed-off-by: default avatarKevin Brodsky <kevin.brodsky@arm.com>
    Reviewed-by: default avatarDave Martin <dave.martin@arm.com>
    Acked-by: default avatarWill Deacon <will.deacon@arm.com>
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    49eea433
gettimeofday.S 8.03 KB