• john stultz's avatar
    time: Introduce CLOCK_REALTIME_COARSE · da15cfda
    john stultz authored
    After talking with some application writers who want very fast, but not
    fine-grained timestamps, I decided to try to implement new clock_ids
    to clock_gettime(): CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE
    which returns the time at the last tick. This is very fast as we don't
    have to access any hardware (which can be very painful if you're using
    something like the acpi_pm clocksource), and we can even use the vdso
    clock_gettime() method to avoid the syscall. The only trade off is you
    only get low-res tick grained time resolution.
    
    This isn't a new idea, I know Ingo has a patch in the -rt tree that made
    the vsyscall gettimeofday() return coarse grained time when the
    vsyscall64 sysctrl was set to 2. However this affects all applications
    on a system.
    
    With this method, applications can choose the proper speed/granularity
    trade-off for themselves.
    Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: nikolag@ca.ibm.com
    Cc: Darren Hart <dvhltc@us.ibm.com>
    Cc: arjan@infradead.org
    Cc: jonathan@jonmasters.org
    LKML-Reference: <1250734414.6897.5.camel@localhost.localdomain>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    da15cfda
vclock_gettime.c 4.17 KB