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    SubjectRe: [PATCH (update 3)] timer: Run calc_load halfway through each round_jiffies second
    Whenever jiffies is started at a multiple of 5*HZ or wraps, calc_load is 
    run exactly on the second which is when tasks using round_jiffies will
    be scheduled to run. This has a bad effect on the load average, making
    it tend towards 1.00 if a task happens to run every time the load is
    being calculated.

    This changes calc_load so that it updates load half a second after any
    tasks scheduled using round_jiffies.

    Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    ---
    This version starts count off at 0, since LOAD_FREQ + HZ/2 is no better
    than LOAD_FREQ. The previous version is actually wrong, rounding count to
    a negative value will only happen when getting calc_load running at the
    right time related to jiffies, it won't be negative running normally -
    even with NO_HZ.

    kernel/timer.c | 8 +++++---
    1 files changed, 5 insertions(+), 3 deletions(-)

    diff --git a/kernel/timer.c b/kernel/timer.c
    index 6663a87..4abead0 100644
    --- a/kernel/timer.c
    +++ b/kernel/timer.c
    @@ -1226,17 +1226,19 @@ EXPORT_SYMBOL(avenrun);
    static inline void calc_load(unsigned long ticks)
    {
    unsigned long active_tasks; /* fixed-point */
    - static int count = LOAD_FREQ;
    + static int count = 0;

    count -= ticks;
    - if (unlikely(count < 0)) {
    + if (unlikely(count <= 0)) {
    active_tasks = count_active_tasks();
    do {
    CALC_LOAD(avenrun[0], EXP_1, active_tasks);
    CALC_LOAD(avenrun[1], EXP_5, active_tasks);
    CALC_LOAD(avenrun[2], EXP_15, active_tasks);
    count += LOAD_FREQ;
    - } while (count < 0);
    + } while (count <= 0);
    +
    + count = round_jiffies_relative(count + HZ/2) - HZ/2;
    }
    }

    --
    1.5.0.1

    --
    Simon Arlott
    -
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