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SubjectRe: [PATCH 1/3] sched, balancing: Update rq->max_idle_balance_cost whenever newidle balance is attempted
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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).

>
> Besides this:
> Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>

Thanks for the review.



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