* Ting Yang <[EMAIL PROTECTED]> wrote: > + s64 __delta = curr->fair_key - p->fair_key; > + > + /* > + * Take scheduling granularity into account - do not > + * preempt the current task unless the best task has > + * a larger than sched_granularity fairness advantage: > + */ > + if (__delta > niced_granularity(rq, curr, granularity)) > + resched_task(curr); > +} > > This code actually now says, the difference of fair_key needed to > preempt the current task is amplified by a facto of its weigh (in Al > Boldi's example 32). However, the weighted task already advance its > p->fair_key by its weight, (also 32 here). The combination of them > becomes quadratic!
it's not quadratic in terms of CPU share: the first factor impacts the CPU share, the second factor impacts the granularity. This means that reniced workloads will be preempted in a more finegrained way - but otherwise there's _no_ quadratic effect for CPU time - which is a completely separate metric. Remember: there are no timeslices in CFS, so a task can be preempted any number of times without being at a disadvantage. > Besides this quadratic effect, another minor issue amplified this > a little bit further: p->wait_runtime accumulated before. [...] actually, this 'minor issue' was the main issue that caused the bug ;-) Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/