Re: [RFC PATCH 3/6] sched/dl: Try better placement even for deadline tasks that do not block

[Morten Rasmussen]

On Tue, May 07, 2019 at 03:13:40PM +0100, Quentin Perret wrote:
> On Monday 06 May 2019 at 06:48:33 (+0200), Luca Abeni wrote:
> > @@ -1591,6 +1626,7 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
> >  
> >  	rcu_read_lock();
> >  	curr = READ_ONCE(rq->curr); /* unlocked access */
> > +	het = static_branch_unlikely(&sched_asym_cpucapacity);
> 
> Nit: not sure how the generated code looks like but I wonder if this
> could potentially make you loose the benefit of the static key ?

I have to take the blame for this bit :-)

I would be surprised the static_key gives us anything here, but that is 
actually not the point here. It is purely to know whether we have to be 
capacity aware or not. I don't think we are in a critical path and the
variable providing the necessary condition just happened to be a
static_key.

We might be able to make better use of it if we refactor the code a bit.

Morten