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    SubjectRe: [PATCH 2/2] sched,time: call __acct_update_integrals once a jiffy
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    On 01/29/2016 05:23 PM, riel@redhat.com wrote:
    > From: Rik van Riel <riel@redhat.com>

    > This speeds up

    ... ok, that changelog got truncated :(

    Here is the full version:


    Because __acct_update_integrals does nothing unless the time
    interval in question exceeds a jiffy, there is no real reason
    to call it more than once a jiffy from the syscall, irq, and
    guest entry & exit paths.

    If tasks get rescheduled frequently, the scheduler will still
    update their time statistics normally.

    However, longer running tasks with frequent syscall, irq,
    or guest entry & exit see a difference with this patch.

    A microbenchmark calling an invalid syscall number 10 million
    times in a row speeds up an additional 30% over the numbers
    with just the previous patch, for a total speedup of about 40%
    over 4.4 and 4.5-rc1.

    Run times for the microbenchmark:

    4.4 3.8 seconds
    4.5-rc1 3.7 seconds
    4.5-rc1 + first patch 3.3 seconds
    4.5-rc1 + both patches 2.3 seconds


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