Re: [PATCH 2/3] sched: introduce per-cpu var next_cpu to track search limit

[Subhra Mazumdar]

On 04/24/2018 05:47 AM, Peter Zijlstra wrote:
> On Mon, Apr 23, 2018 at 05:41:15PM -0700, subhra mazumdar wrote:
> > @@ -17,6 +17,7 @@
> >   #include <trace/events/sched.h>
> >   
> >   DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
> > +DEFINE_PER_CPU_SHARED_ALIGNED(int, next_cpu);
> >   
> >   #if defined(CONFIG_SCHED_DEBUG) && defined(HAVE_JUMP_LABEL)
> >   /*
> > @@ -6018,6 +6019,7 @@ void __init sched_init(void)
> >   		struct rq *rq;
> >   
> >   		rq = cpu_rq(i);
> > +		per_cpu(next_cpu, i) = -1;
> If you leave it uninitialized it'll be 0, and we can avoid that extra
> branch in the next patch, no?
0 can be a valid cpu id. I wanted to distinguish the first time. The branch
predictor will be fully trained so will not have any cost.