Kirill Tkhai <[email protected]> writes: > В Вт, 24/06/2014 в 23:26 +0400, Kirill Tkhai пишет: >> On 24.06.2014 23:13, [email protected] wrote: >> > Kirill Tkhai <[email protected]> writes: >> > >> >> On 24.06.2014 21:03, [email protected] wrote: >> >>> Kirill Tkhai <[email protected]> writes: >> >>> >> >>>> We kill rq->rd on the CPU_DOWN_PREPARE stage: >> >>>> >> >>>> cpuset_cpu_inactive -> cpuset_update_active_cpus -> >> >>>> partition_sched_domains -> >> >>>> -> cpu_attach_domain -> rq_attach_root -> set_rq_offline >> >>>> >> >>>> This unthrottles all throttled cfs_rqs. >> >>>> >> >>>> But the cpu is still able to call schedule() till >> >>>> >> >>>> take_cpu_down->__cpu_disable() >> >>>> >> >>>> is called from stop_machine. >> >>>> >> >>>> This case the tasks from just unthrottled cfs_rqs are pickable >> >>>> in a standard scheduler way, and they are picked by dying cpu. >> >>>> The cfs_rqs becomes throttled again, and migrate_tasks() >> >>>> in migration_call skips their tasks (one more unthrottle >> >>>> in migrate_tasks()->CPU_DYING does not happen, because rq->rd >> >>>> is already NULL). >> >>>> >> >>>> Patch sets runtime_enabled to zero. This guarantees, the runtime >> >>>> is not accounted, and the cfs_rqs won't exceed given >> >>>> cfs_rq->runtime_remaining = 1, and tasks will be pickable >> >>>> in migrate_tasks(). runtime_enabled is recalculated again >> >>>> when rq becomes online again. >> >>>> >> >>>> Ben Segall also noticed, we always enable runtime in >> >>>> tg_set_cfs_bandwidth(). Actually, we should do that for online >> >>>> cpus only. To fix that, we check if a cpu is online when >> >>>> its rq is locked. This guarantees we do not have races with >> >>>> set_rq_offline(), which also requires rq->lock. >> >>>> >> >>>> v2: Fix race with tg_set_cfs_bandwidth(). >> >>>> Move cfs_rq->runtime_enabled=0 above unthrottle_cfs_rq(). >> >>>> >> >>>> Signed-off-by: Kirill Tkhai <[email protected]> >> >>>> CC: Konstantin Khorenko <[email protected]> >> >>>> CC: Ben Segall <[email protected]> >> >>>> CC: Paul Turner <[email protected]> >> >>>> CC: Srikar Dronamraju <[email protected]> >> >>>> CC: Mike Galbraith <[email protected]> >> >>>> CC: Peter Zijlstra <[email protected]> >> >>>> CC: Ingo Molnar <[email protected]> >> >>>> --- >> >>>> kernel/sched/core.c | 15 +++++++++++---- >> >>>> kernel/sched/fair.c | 22 ++++++++++++++++++++++ >> >>>> 2 files changed, 33 insertions(+), 4 deletions(-) >> >>>> >> >>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> >>>> index 7f3063c..707a3c5 100644 >> >>>> --- a/kernel/sched/core.c >> >>>> +++ b/kernel/sched/core.c >> >>>> @@ -7842,11 +7842,18 @@ static int tg_set_cfs_bandwidth(struct >> >>>> task_group *tg, u64 period, u64 quota) >> >>>> struct rq *rq = cfs_rq->rq; >> >>>> >> >>>> raw_spin_lock_irq(&rq->lock); >> >>>> - cfs_rq->runtime_enabled = runtime_enabled; >> >>>> - cfs_rq->runtime_remaining = 0; >> >>>> + /* >> >>>> + * Do not enable runtime on offline runqueues. We >> >>>> specially >> >>>> + * make it disabled in unthrottle_offline_cfs_rqs(). >> >>>> + */ >> >>>> + if (cpu_online(i)) { >> >>>> + cfs_rq->runtime_enabled = runtime_enabled; >> >>>> + cfs_rq->runtime_remaining = 0; >> >>>> + >> >>>> + if (cfs_rq->throttled) >> >>>> + unthrottle_cfs_rq(cfs_rq); >> >>>> + } >> >>> >> >>> We can just do for_each_online_cpu, yes? Also we probably need >> >>> get_online_cpus/put_online_cpus, and/or want cpu_active_mask instead >> >>> right? >> >>> >> >> >> >> Yes, we can use for_each_online_cpu/for_each_active_cpu with >> >> get_online_cpus() taken. But it adds one more lock dependence. >> >> This looks worse for me. >> > >> > I mean, you need get_online_cpus anyway - cpu_online is just a test >> > against the same mask that for_each_online_cpu uses, and without taking >> > the lock you can still race with offlining and reset runtime_enabled. >> > >> >> Oh, I see. Thanks. > > But we can check for rq->online, don't we? How about this?
Yeah, that should work. > > sched/fair: Disable runtime_enabled on dying rq > > We kill rq->rd on the CPU_DOWN_PREPARE stage: > > cpuset_cpu_inactive -> cpuset_update_active_cpus -> > partition_sched_domains -> > -> cpu_attach_domain -> rq_attach_root -> set_rq_offline > > This unthrottles all throttled cfs_rqs. > > But the cpu is still able to call schedule() till > > take_cpu_down->__cpu_disable() > > is called from stop_machine. > > This case the tasks from just unthrottled cfs_rqs are pickable > in a standard scheduler way, and they are picked by dying cpu. > The cfs_rqs becomes throttled again, and migrate_tasks() > in migration_call skips their tasks (one more unthrottle > in migrate_tasks()->CPU_DYING does not happen, because rq->rd > is already NULL). > > Patch sets runtime_enabled to zero. This guarantees, the runtime > is not accounted, and the cfs_rqs won't exceed given > cfs_rq->runtime_remaining = 1, and tasks will be pickable > in migrate_tasks(). runtime_enabled is recalculated again > when rq becomes online again. > > Ben Segall also noticed, we always enable runtime in > tg_set_cfs_bandwidth(). Actually, we should do that for online > cpus only. To fix that, we check if a cpu is online when > its rq is locked. This guarantees we do not have races with > set_rq_offline(), which also requires rq->lock. > > v2: Fix race with tg_set_cfs_bandwidth(). > Move cfs_rq->runtime_enabled=0 above unthrottle_cfs_rq(). > v3: Check for rq->online instead of cpu_active. > > Signed-off-by: Kirill Tkhai <[email protected]> Reviewed-by: Ben Segall <[email protected]> -- 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/
