On 05/09/2013 05:30 PM, Paul Turner wrote: >> > With sched_slice, we need to set the runnable avg sum/period after new >> > task assigned to a specific CPU. >> > So, set them __sched_fork is meaningless. and then > This is still a reasonable choice. > > Assuming the system is well balanced, sched_slice() on the current CPU > should be reasonably indicative of the slice wherever we end up. The > alternative is still to pick a constant. We should do one of these. > >> > __update_task_entity_contrib(&p->se) also no reason to use. > Surely we'd still want it so that the right load is added by > enqueue_entity_load_avg()? >
thanks for comments! the new patch attached, hope it is your liked this time. :) --- >From 5606df1e46e83e64b0ade30522096c00448a97be Mon Sep 17 00:00:00 2001 From: Alex Shi <alex....@intel.com> Date: Mon, 3 Dec 2012 17:30:39 +0800 Subject: [PATCH 3/7] sched: set initial value of runnable avg for new forked task We need initialize the se.avg.{decay_count, load_avg_contrib} for a new forked task. Otherwise random values of above variables cause mess when do new task enqueue: enqueue_task_fair enqueue_entity enqueue_entity_load_avg and make forking balancing imbalance since incorrect load_avg_contrib. Further more, Morten Rasmussen notice some tasks were not launched at once after created. So Paul and Peter suggest giving a start value for new task runnable avg time same as sched_slice(). Signed-off-by: Alex Shi <alex....@intel.com> --- kernel/sched/core.c | 6 ++---- kernel/sched/fair.c | 23 +++++++++++++++++++++++ kernel/sched/sched.h | 2 ++ 3 files changed, 27 insertions(+), 4 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c8db984..866c05a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1563,10 +1563,6 @@ static void __sched_fork(struct task_struct *p) p->se.vruntime = 0; INIT_LIST_HEAD(&p->se.group_node); -#ifdef CONFIG_SMP - p->se.avg.runnable_avg_period = 0; - p->se.avg.runnable_avg_sum = 0; -#endif #ifdef CONFIG_SCHEDSTATS memset(&p->se.statistics, 0, sizeof(p->se.statistics)); #endif @@ -1710,6 +1706,8 @@ void wake_up_new_task(struct task_struct *p) set_task_cpu(p, select_task_rq(p, SD_BALANCE_FORK, 0)); #endif + /* Give new task start runnable values */ + set_task_runnable_avg(p); rq = __task_rq_lock(p); activate_task(rq, p, 0); p->on_rq = 1; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9c2f726..203f236 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -661,6 +661,26 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se) return calc_delta_fair(sched_slice(cfs_rq, se), se); } +#ifdef CONFIG_SMP +static inline void __update_task_entity_contrib(struct sched_entity *se); + +/* Give new task start runnable values to heavy its load in infant time */ +void set_task_runnable_avg(struct task_struct *p) +{ + u32 slice; + + p->se.avg.decay_count = 0; + slice = sched_slice(task_cfs_rq(p), &p->se) >> 10; + p->se.avg.runnable_avg_sum = slice; + p->se.avg.runnable_avg_period = slice; + __update_task_entity_contrib(&p->se); +} +#else +void set_task_runnable_avg(struct task_struct *p) +{ +} +#endif + /* * Update the current task's runtime statistics. Skip current tasks that * are not in our scheduling class. @@ -1508,6 +1528,9 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq, * We track migrations using entity decay_count <= 0, on a wake-up * migration we use a negative decay count to track the remote decays * accumulated while sleeping. + * + * When enqueue a new forked task, the se->avg.decay_count == 0, so + * we bypass update_entity_load_avg(), use avg.load_avg_contrib direct. */ if (unlikely(se->avg.decay_count <= 0)) { se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c6634f1..518f3d8a 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -900,6 +900,8 @@ extern void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime extern void update_idle_cpu_load(struct rq *this_rq); +extern void set_task_runnable_avg(struct task_struct *p); + #ifdef CONFIG_CGROUP_CPUACCT #include <linux/cgroup.h> /* track cpu usage of a group of tasks and its child groups */ -- 1.7.5.4 -- 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/