Re: [RFCv3 PATCH 45/48] sched: Skip cpu as lb src which has one task and capacity gte the dst cpu

[Dietmar Eggemann]

On 24/03/15 15:27, Peter Zijlstra wrote:
> On Wed, Feb 04, 2015 at 06:31:22PM +0000, Morten Rasmussen wrote:
> > From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> >
> > Skip cpu as a potential src (costliest) in case it has only one task
> > running and its original capacity is greater than or equal to the
> > original capacity of the dst cpu.
>
> Again, that's what, but is lacking a why.

You're right, the 'why' is completely missing.

This is one of our heterogeneous (big.LITTLE) cpu related patches. We 
don't want to end up migrating this single task from a big to a little 
cpu, hence the use of capacity_orig_of(cpu). Our cpu topology makes sure 
that this rule is only active on DIE sd level.

We could replace the use of capacity_orig_of(cpu) w/ capacity_of(cpu) to 
take big.LITTLE and RT and/or IRQ work into consideration which then 
would effect the MC sd level too.

Will add the 'why' in the next version.

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