On 12/06/2012 11:10 PM, Alex Shi wrote: > >>> Hi Paul & Ingo: >>> >>> In a short word of this issue: burst forking/waking tasks have no time >>> accumulate the load contribute, their runnable load are taken as zero. >>> that make select_task_rq do a wrong decision on which group is idlest. >> >> So these aren't strictly comparable; bursting and forking tasks have >> fairly different characteristics here. > > Many thanks for looking into this. :) >> >> When we fork a task we intentionally reset the previous history. This >> means that a forked task that immediately runs is going to show up as >> 100% runnable and then converge to it's true value. This was fairly >> intentionally chosen so that tasks would "start" fast rather than >> having to worry about ramp up. > > I am sorry for didn't see the 100% runnable for a new forked task. > I believe the code need the following patch to initialize decay_count, > and load_avg_contrib. otherwise they are random value. > In enqueue_entity_load_avg() p->se.avg.runnable_avg_sum for new forked > task is always zero, either because se.avg.last_runnable_update is set > as clock_task due to decay_count <=0, or just do > __synchronize_entity_decay not update_entity_load_avg.
Paul: Would you like to give some comments for the following patches? > > =========== > From a161000dbece6e95bf3b81e9246d51784589d393 Mon Sep 17 00:00:00 2001 > From: Alex Shi <alex....@intel.com> > Date: Mon, 3 Dec 2012 17:30:39 +0800 > Subject: [PATCH 05/12] sched: load tracking bug fix > > We need initialize the se.avg.{decay_count, load_avg_contrib} to zero > after a new task forked. > Otherwise random values of above variable give a incorrect statistic > data when do new task enqueue: > enqueue_task_fair > enqueue_entity > enqueue_entity_load_avg > > Signed-off-by: Alex Shi <alex....@intel.com> > --- > kernel/sched/core.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 5dae0d2..e6533e1 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1534,6 +1534,8 @@ static void __sched_fork(struct task_struct *p) > #if defined(CONFIG_SMP) && defined(CONFIG_FAIR_GROUP_SCHED) > p->se.avg.runnable_avg_period = 0; > p->se.avg.runnable_avg_sum = 0; > + p->se.avg.decay_count = 0; > + p->se.avg.load_avg_contrib = 0; > #endif > #ifdef CONFIG_SCHEDSTATS > memset(&p->se.statistics, 0, sizeof(p->se.statistics)); > -- Thanks Alex -- 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/