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    SubjectRe: [3.2.16 -> 3.2.17 regression] High reported CPU load when idle
    Hi Doug et al,

    Doug Smythies wrote:

    > "does 556061b00c9f ("sched/nohz: Fix rq->cpu_load[] calculations",
    > 2012-05-11) change anything?"
    >
    > I back edited those changes into my test environment yesterday. It
    > made no difference with respect to this issue. (minimally tested.)
    [...]
    > By the way, I found and tested 5aaa0b7a2ed5b12692c9ffb5222182bd558d3146
    > It is similar (minimally tested).
    >
    > I am certainly not an expert, and I find the load average area of the
    > code extremely difficult to follow and understand. That being said, I
    > think the root issue here is the 10 tick grace period. I think that
    > cpu idle enter exit transitions can not be ignored during this period,
    > and somehow needs to be accumulated towards the next sample time. So far,
    > I have been unsuccessful trying to help with a suggested solution. I will
    > continue to try.

    Another load average related patch is being discussed (not meant
    particularly to address the too-low load case, just mentioning it
    FYI):

    sched: Folding nohz load accounting more accurate

    After patch 453494c3d4 (sched: Fix nohz load accounting -- again!), we can fold
    the idle into calc_load_tasks_idle between the last cpu load calculating and
    calc_global_load calling. However problem still exits between the first cpu
    load calculating and the last cpu load calculating. Every time when we do load
    calculating, calc_load_tasks_idle will be added into calc_load_tasks, even if
    the idle load is caused by calculated cpus. This problem is also described in
    the following link:

    https://lkml.org/lkml/2012/5/24/419

    This bug can be found in our work load. The average running processes number
    is about 15, but the load only shows about 4.

    From [*].

    Hope that helps,
    Jonathan

    [*] http://thread.gmane.org/gmane.linux.kernel/1310462


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