On Mon, 2013-07-22 at 12:31 +0530, Srikar Dronamraju wrote: > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index e8b3350..da2cb3e 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -1348,6 +1348,8 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, > > int wake_flags) > > else > > update_avg(&rq->avg_idle, delta); > > rq->idle_stamp = 0; > > + > > + rq->idle_duration = (rq->idle_duration + delta) / 2; > > Cant we just use avg_idle instead of introducing idle_duration?
A potential issue I have found with avg_idle is that it may sometimes be not quite as accurate for the purposes of this patch, because it is always given a max value (default is 1000000 ns). For example, a CPU could have remained idle for 1 second and avg_idle would be set to 1 millisecond. Another question I have is whether we can update avg_idle at all times without putting a maximum value on avg_idle, or increase the maximum value of avg_idle by a lot. > Should we take the consideration of whether a idle_balance was > successful or not? I recently ran fserver on the 8 socket machine with HT-enabled and found that load balance was succeeding at a higher than average rate, but idle balance was still lowering performance of that workload by a lot. However, it makes sense to allow idle balance to run longer/more often when it has a higher success rate. > I am not sure whats a reasonable value for n can be, but may be we could > try with n=3. Based on some of the data I collected, n = 10 to 20 provides much better performance increases. > Also have we checked the performance after adjusting the > sched_migration_cost tunable? > > I guess, if we increase the sched_migration_cost, we should have lesser > newly idle balance requests. Yes, I have done quite a bit of testing with sched_migration_cost and adjusting it does help performance when idle balance overhead is high. But I have found that a higher value may decrease the performance during situations where the cost of idle_balance is not high. Additionally, when to modify this tunable and by how much to modify it by can sometimes be unpredictable. Thanks, Jason -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
