(I'm still in New Zealand and won't be on regular email until March 6th, but I just saw this and wanted to comment quickly)
On Thu, Feb 28, 2013 at 7:26 PM, Namhyung Kim <namhy...@kernel.org> wrote: > From: Namhyung Kim <namhyung....@lge.com> > > The calc_tg_weight() and calc_cfs_shares() used cfs_rq->load.weight > but this is no longer valid for per-entity load tracking since > cfs_rq->tg_load_contrib consists of runnable_load_avg and blocked_ > load_avg. Simply using load.weight here will lose blocked_load_avg > part so will result in an inaccurate share. > > Cc: Paul Turner <p...@google.com> > Signed-off-by: Namhyung Kim <namhy...@kernel.org> > --- > kernel/sched/fair.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 7a33e5986fc5..add7440bd02f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1032,13 +1032,13 @@ static inline long calc_tg_weight(struct task_group > *tg, struct cfs_rq *cfs_rq) > long tg_weight; > > /* > - * Use this CPU's actual weight instead of the last load_contribution > - * to gain a more accurate current total weight. See > - * update_cfs_rq_load_contribution(). > + * Use this CPU's actual load instead of the last load_contribution > + * to gain a more accurate current total load. See > + * __update_cfs_rq_tg_load_contrib(). > */ > tg_weight = atomic64_read(&tg->load_avg); > tg_weight -= cfs_rq->tg_load_contrib; > - tg_weight += cfs_rq->load.weight; > + tg_weight += cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg; No -- we _really_ do want to use the instantaneous weight, the maintained averages are back-wards looking and do not always predict future usage. We played with allocation strategies like the above during this development and it ends up being a big loss for latency. In particular: tasks with a low runnable averages are almost always going to be _under_ their fair share; using the current runnable average here then harshly penalizes their ability to pre-empt when the calculated weight is subsequently used for emplacement. Stronger: Such tasks are typically interactive (having to wait for us slow humans and all). Consider what the above would do to a while(1) versus interactive thread in the same cgroup; the cpu holding the while(1) thread is always going to wholly dominate share allocation. > return tg_weight; > } > @@ -1048,7 +1048,7 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq, > struct task_group *tg) > long tg_weight, load, shares; > > tg_weight = calc_tg_weight(tg, cfs_rq); > - load = cfs_rq->load.weight; > + load = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg; > > shares = (tg->shares * load); > if (tg_weight) > -- > 1.7.11.7 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
