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    SubjectRe: sched_clock() uses are broken
    On Wed, 3 May 2006, George Anzinger wrote:

    > Nicolas Pitre wrote:
    > > Yet that counter isn't necessarily nanosecond based. So rescaling the
    > > returned value to nanosecs requires expensive divisions which could be done
    > > only once within sched_clock_diff() instead of twice as often in each
    > > sched_clock() calls.
    >
    > Oh phooey!! Scaling can be done with a mpy and a shift. See the new clock
    > code where the TSC (or what ever) is scaled to ns.

    I know.

    And if you want to preserve more than 32 bits of precision you need 4
    mpy_and_add insns with a shift on ARM at least.

    But the point remains that it is more efficient to do it once rather
    than twice or more.


    Nicolas
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