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. -- 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/
