Re: [PATCH] sched: fix wrong rq's runnable_avg update with rt task

[Vincent Guittot]

On 8 February 2013 15:46, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> On Fri, 2013-02-08 at 12:11 +0100, Vincent Guittot wrote:
>> When a RT task is scheduled on an idle CPU, the update of the rq's load is
>> not done because CFS's functions are not called. Then, the idle_balance,
>> which is called just before entering the idle function, updates the
>> rq's load and makes the assumption that the elapsed time since the last
>> update, was only running time.
>>
>> The rq's load of a CPU that only runs a periodic RT task, is close to
>> LOAD_AVG_MAX whatever the running duration of the RT task is.
>>
>> A new idle_exit function is called when the prev task is the idle function
>> so the elapsed time will be accounted as idle time in the rq's load.
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>> ---
>>  kernel/sched/core.c  |    3 +++
>>  kernel/sched/fair.c  |   10 ++++++++++
>>  kernel/sched/sched.h |    5 +++++
>>  3 files changed, 18 insertions(+)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 26058d0..592e06c 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2927,6 +2927,9 @@ need_resched:
>>
>>       pre_schedule(rq, prev);
>>
>> +     if (unlikely(prev == rq->idle))
>> +             idle_exit(cpu, rq);
>> +
>
> Let's get rid of the added junk in the core code that should be isolated
> in the idle code.
>

i agree

> I posted these patches before, and I'm about to post again:
>
> https://lkml.org/lkml/2012/12/21/378
> https://lkml.org/lkml/2012/12/21/377
>
> I'm working to clean these patches up today and post them again. Would
> working on top of these work for you?

yes for sure.
I will move that code in pre_schedule

Vincent

>
> -- Steve
>
>
>>       if (unlikely(!rq->nr_running))
>>               idle_balance(cpu, rq);
>>
>
>
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