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    SubjectRE: Regression seen for patch "sched:dont decrease idle sleep avg"
    Date
    Con Kolivas wrote on Wednesday, May 17, 2006 10:52 PM
    > The relationship between INTERACTIVE_SLEEP and the ceiling is not perfect
    > and not explicit enough. The sleep boost is not supposed to be any larger
    > than without this code and the comment is not clear enough about what exactly
    > it does, just the reason it does it.
    >
    > There is a ceiling to the priority beyond which tasks that only ever sleep
    > for very long periods cannot surpass.
    >
    > Opportunity to micro-optimise and re-use the ceiling variable.
    >
    > --- linux-2.6.17-rc4-mm1.orig/kernel/sched.c 2006-05-17 15:57:49.000000000 +1000
    > +++ linux-2.6.17-rc4-mm1/kernel/sched.c 2006-05-18 15:48:47.000000000 +1000
    > @@ -925,12 +924,12 @@ static int recalc_task_prio(task_t *p, u
    > * are likely to be waiting on I/O
    > */
    > if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
    > - if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
    > + if (p->sleep_avg >= ceiling)
    > sleep_time = 0;
    > else if (p->sleep_avg + sleep_time >=
    > - INTERACTIVE_SLEEP(p)) {
    > - p->sleep_avg = INTERACTIVE_SLEEP(p);
    > - sleep_time = 0;
    > + ceiling) {
    > + p->sleep_avg = ceiling;
    > + sleep_time = 0;


    Watch for white space damage, last two lines has one extra tab on the indentation.


    By the way, there is all kinds of non-linear behavior with priority boost
    adjustment:

    if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
    if (p->sleep_avg >= ceiling)
    sleep_time = 0;
    else if (p->sleep_avg + sleep_time >= ceiling) {
    p->sleep_avg = ceiling;
    sleep_time = 0;
    }
    }

    For large p->sleep_avg, kernel don't clamp it to ceiling, yet clamp small
    incremental sleep. This all seems very fragile.

    - Ken
    -
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