Messages in this thread | | | From | bsegall@google ... | Subject | Re: [PATCH v2 1/3] sched/fair: Disable runtime_enabled on dying rq | Date | Wed, 25 Jun 2014 10:40:48 -0700 |
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Kirill Tkhai <ktkhai@parallels.com> writes:
> В Ср, 25/06/2014 в 09:52 -0700, bsegall@google.com пишет: >> Kirill Tkhai <ktkhai@parallels.com> writes: >> >> > В Вт, 24/06/2014 в 23:26 +0400, Kirill Tkhai пишет: >> >> On 24.06.2014 23:13, bsegall@google.com wrote: >> >> > Kirill Tkhai <tkhai@yandex.ru> writes: >> >> > >> >> >> On 24.06.2014 21:03, bsegall@google.com wrote: >> >> >>> Kirill Tkhai <ktkhai@parallels.com> 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 <ktkhai@parallels.com> >> >> >>>> CC: Konstantin Khorenko <khorenko@parallels.com> >> >> >>>> CC: Ben Segall <bsegall@google.com> >> >> >>>> CC: Paul Turner <pjt@google.com> >> >> >>>> CC: Srikar Dronamraju <srikar@linux.vnet.ibm.com> >> >> >>>> CC: Mike Galbraith <umgwanakikbuti@gmail.com> >> >> >>>> CC: Peter Zijlstra <peterz@infradead.org> >> >> >>>> CC: Ingo Molnar <mingo@kernel.org> >> >> >>>> --- >> >> >>>> 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. > > We can't base on it because rq->offline is not available in !SMP. > Could you review the message from [PATCH v3 1/3] topic?
I'm not sure what you mean here. The patch just checking cpu_online won't work, is there another version you want me to look at? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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