Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator

[Dietmar Eggemann]

On 08/06/2018 02:37 PM, Vincent Guittot wrote:
> On Mon, 6 Aug 2018 at 14:29, Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
> > On 08/06/2018 12:33 PM, Vincent Guittot wrote:
> > > On Mon, 6 Aug 2018 at 12:08, Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
> > > > On 08/06/2018 10:40 AM, Vincent Guittot wrote:
> > > > > On Fri, 3 Aug 2018 at 17:55, Quentin Perret <quentin.perret@xxxxxxx> wrote:
> > > > > > On Friday 03 Aug 2018 at 15:49:24 (+0200), Vincent Guittot wrote:
> > > > > > > On Fri, 3 Aug 2018 at 10:18, Quentin Perret <quentin.perret@xxxxxxx> wrote:
> > > > > > > > On Friday 03 Aug 2018 at 09:48:47 (+0200), Vincent Guittot wrote:
> > > > > > > > > On Thu, 2 Aug 2018 at 18:59, Quentin Perret <quentin.perret@xxxxxxx> wrote:
> > > >
> > > > [...]
> > > >
> > > > > > I think we're discussing two different things right now:
> > > > > >        1. Should forkees go in find_energy_efficient_cpu() ?
> > > > > >        2. Should forkees have 0 of initial util_avg when EAS is enabled ?
> > > > >
> > > > > It's the same topic: How EAS should consider a newly created task ?
> > > > >
> > > > > For now, we let the "performance" mode selects a CPU. This CPU will
> > > > > most probably be worst CPU from a EAS pov because it's the idlest CPU
> > > > > in the idlest group which is the opposite of what EAS tries to do
> > > > >
> > > > > The current behavior is :
> > > > > For every new task, the cpu selection is done assuming it's a heavy
> > > > > task with the max possible load_avg,  and it looks for the idlest cpu.
> > > > > This means that if the system is lightly loaded, scheduler will select
> > > > > most probably a idle big core.
> > > >
> > > > AFAICS, task load doesn't seem to be used for find_idlest_cpu() (
> > > > find_idlest_group() and find_idlest_group_cpu()). So the forkee
> > > > (SD_BALANCE_FORK) is placed independently of his task load.
> > >
> > > hmm ... so what is used if load or runnable load are not used ?
> > > find_idlest_group() uses load and runnable load but skip spare
> > > capacity in case of fork
> >
> > Yes, runnable load and load are used, but from the cpus, not from the task.
>
> yes that's right, I have skipped the "task" word when reading.
> So scheduler looks for the idlest CPU taking into account only CPU
> loads. Then the task load starts to highest value until it get a
> chance to reduce and stabilize to its final value

This could potentially allow us to find a better init value for 
sa->[runnable]_load_avg. At least we could use the information of the 
initial task rq.

> > [...]