Messages in this thread | | | Subject | Re: [PATCH] sched: Reduce the rate of needless idle load balancing | From | Tim Chen <> | Date | Wed, 21 May 2014 11:49:59 -0700 |
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On Wed, 2014-05-21 at 11:26 -0700, Davidlohr Bueso wrote: > On Wed, 2014-05-21 at 09:37 -0700, Tim Chen wrote: > > On Tue, 2014-05-20 at 18:15 -0700, Joe Perches wrote: > > > On Tue, 2014-05-20 at 14:04 -0700, Tim Chen wrote: > > > > On Tue, 2014-05-20 at 13:59 -0700, Tim Chen wrote: > > > > > On Tue, 2014-05-20 at 13:51 -0700, Jason Low wrote: > > > > > > On Tue, May 20, 2014 at 1:17 PM, Tim Chen <tim.c.chen@linux.intel.com> wrote: > > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > [] > > > > > > If we want to do idle load balancing only when it is due for a > > > > > > balance, shouldn't the above just be "if (time_after(jiffies, > > > > > > rq->next_balance))"? > > > > > > > > > > If rq->next_balance and jiffies are equal, then > > > > > time_after(jiffies, rq->next_balance) check will be false and > > > > > you will not do balance. But actually you want to balance > > > > > for this case so the jiffies+1 was used. > > > > > > > > So maybe I should switch the check to > > > > if (time_before(rq->next_balance, jiffies)) > > > > > > time_after_eq() or time_is_after_eq_jiffies() > > > > > > > > > > I prefer time_after_eq to keep the code style consistent with the > > rest of the code in fair.c. > > Should all the code be updated then? We should use the existing > interfaces if available. >
BTW, if this code was to be updated, time_is_before_eq_jiffies(rq->next_balance) check will be the correct thing to do for the patch. This expands to time_after_eq(jiffies, rq->next_balance), which is what we want.
So something like:
if (time_is_before_eq_jiffies(rq->next_balance)) { raw_spin_lock_irq(&rq->lock); update_rq_clock(rq); update_idle_cpu_load(rq); raw_spin_unlock_irq(&rq->lock); rebalance_domains(rq, CPU_IDLE); }
But I don't think this change is making the code logic any clearer. I prefer time_after_eq(jiffies, rq->next_balance), which is more readable.
Tim
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