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    SubjectRe: [PATCH 1/3] sched, balancing: Update rq->max_idle_balance_cost whenever newidle balance is attempted
    On 04/28/2014 11:34 PM, Jason Low wrote:
    > On Sun, 2014-04-27 at 14:01 +0530, Preeti Murthy wrote:
    >> Hi Jason, Peter,
    >>
    >> The below patch looks good to me except for one point.
    >>
    >> In idle_balance() the below code snippet does not look right:
    >>
    >> - if (pulled_task || time_after(jiffies, this_rq->next_balance)) {
    >> - /*
    >> - * We are going idle. next_balance may be set based on
    >> - * a busy processor. So reset next_balance.
    >> - */
    >> +out:
    >> + /* Move the next balance forward */
    >> + if (time_after(this_rq->next_balance, next_balance))
    >> this_rq->next_balance = next_balance;
    >> - }
    >>
    >> By not checking this_rq->next_balance against jiffies,
    >> we might end up not updating this parameter when it
    >> has expired.
    >>
    >> So shouldn't it be:
    >>
    >> if (time_after(jiffies, this_rq->next_balance) ||
    >> time_after(this_rq->next_balance, next_balance))
    >> this_rq->next_balance = next_balance;
    >
    > Hi Preeti,
    >
    > If jiffies is after this_rq->next_balance, doesn't that mean that it's
    > actually due for a periodic balance and we wouldn't need to modify it?
    > In rebalance_domains(), we do load_balance if time_after_eq(jiffies,
    > sd->last_balance + interval).

    Right. So I missed the point that we don't really have a problem with
    the rq->next_balance being expired. It will anyway ensure that in the
    next call to rebalance_domains() load balancing will be done and that is
    all we want. Thanks for pointing it out.

    Regards
    Preeti U Murthy
    >
    >>
    >> Besides this:
    >> Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
    >
    > Thanks for the review.
    >



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