On Wed, Nov 11, 2015 at 10:26:32AM +0100, Peter Zijlstra wrote:
> On Wed, Nov 11, 2015 at 05:50:27PM +0900, byungchul.p...@lge.com wrote:
>
> I've not actually read anything; my brain isn't working right today.
>
> > +static inline void vruntime_unnormalize(struct cfs_rq *cfs_rq, struct
> > sched_entity *se)
> > +{
> > + se->vruntime += cfs_rq->min_vruntime;
> > + if (unlikely((s64)se->vruntime < 0))
> > + se->vruntime = 0;
> > +}
>
> But this is broken. This simply _cannot_ be right.
>
> vruntime very much needs to wrap in u64 space. While regular time in ns
> takes some 584 year to wrap, vruntime is scaled. The fastest vruntime is
> 2/1024 or 512 times faster than normal time. Making it take just over a
> year to wrap around. This will happen.
Then, do you mean it's no problem even if we compare between a vruntime
not wrapped yet and another vruntime already wrapped? I really wonder it.
>
>
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