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Message-ID: <20150324094345.GA4146@kernel>
Date: Tue, 24 Mar 2015 17:43:45 +0800
From: Wanpeng Li <wanpeng.li@...ux.intel.com>
To: Juri Lelli <juri.lelli@....com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"juri.lelli@...il.com" <juri.lelli@...il.com>,
Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [PATCH RESEND v10] sched/deadline: support dl task migration
during cpu hotplug
On Tue, Mar 24, 2015 at 10:00:25AM +0000, Juri Lelli wrote:
>On 24/03/15 09:13, Wanpeng Li wrote:
>> Hi Juri,
>> On Tue, Mar 24, 2015 at 09:27:09AM +0000, Juri Lelli wrote:
>>> Hi,
>>>
>>> On 23/03/2015 08:55, Peter Zijlstra wrote:
>>>> On Mon, Mar 23, 2015 at 08:25:04AM +0100, Ingo Molnar wrote:
>>>>>>>>>>>> + if (cpu >= nr_cpu_ids) {
>>>>>>>>>>>> + if (dl_bandwidth_enabled()) {
>>>>>>>>>>>> + /*
>>>>>>>>>>>> + * Fail to find any suitable cpu.
>>>>>>>>>>>> + * The task will never come back!
>>>>>>>>>>>> + */
>>>>>>>>>>>> + WARN_ON(1);
>>>>>>>>>>>
>>>>>>>>>>> Can this condition happen to users with a non-buggy kernel?
>>>>
>>>>> I still haven't seen a satisfactory answer to this question. Please
>>>>> don't resend patches without clearing questions raised during review.
>>>>
>>>> So I had a look on Friday, it _should_ not happen, but it does due to a
>>>> second bug Juri is currently chasing down.
>>>>
>>>
>>> Right, it should not happen. It happens because hotplug operations are
>>> destructive w.r.t. cpusets. Peter, how about we move the check you put
>>> in sched_cpu_inactive() to cpuset_cpu_inactive()? This way, if we fail,
>>> we don't need to destroy/rebuild the domains.
>>
>> I remember you mentioned that there is a bug through IRC last week, if this
>> patch solve it?
>>
>
>It seems to fix it. With the previous check we correctly fail to turn
>off a cpu with -dl task running only the first time. After that the
>bandwidth information associated with it was gone and subsequent hotplug
>operations on the same cpu would turn it off.
Cool, thanks for your patch and efforts. ;-)
Regards,
Wanpeng Li
>
>Thanks,
>
>- Juri
>
>> Regards,
>> Wanpeng Li
>>
>>>
>>> Thanks,
>>>
>>> - Juri
>>>
>>> >From 65e8033e05f8b70116747062d00d5a5c266699fb Mon Sep 17 00:00:00 2001
>>> From: Juri Lelli <juri.lelli@...il.com>
>>> Date: Tue, 24 Mar 2015 07:47:03 +0000
>>> Subject: [PATCH] sched/core: check for available -dl bandwidth in
>>> cpuset_cpu_inactive
>>>
>>> Signed-off-by: Juri Lelli <juri.lelli@....com>
>>> ---
>>> kernel/sched/core.c | 56 ++++++++++++++++++++++++++---------------------------
>>> 1 file changed, 28 insertions(+), 28 deletions(-)
>>>
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index 50927eb..3723ad0 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -5318,36 +5318,13 @@ static int sched_cpu_active(struct notifier_block *nfb,
>>> static int sched_cpu_inactive(struct notifier_block *nfb,
>>> unsigned long action, void *hcpu)
>>> {
>>> - unsigned long flags;
>>> - long cpu = (long)hcpu;
>>> - struct dl_bw *dl_b;
>>> -
>>> switch (action & ~CPU_TASKS_FROZEN) {
>>> case CPU_DOWN_PREPARE:
>>> - set_cpu_active(cpu, false);
>>> -
>>> - /* explicitly allow suspend */
>>> - if (!(action & CPU_TASKS_FROZEN)) {
>>> - bool overflow;
>>> - int cpus;
>>> -
>>> - rcu_read_lock_sched();
>>> - dl_b = dl_bw_of(cpu);
>>> -
>>> - raw_spin_lock_irqsave(&dl_b->lock, flags);
>>> - cpus = dl_bw_cpus(cpu);
>>> - overflow = __dl_overflow(dl_b, cpus, 0, 0);
>>> - raw_spin_unlock_irqrestore(&dl_b->lock, flags);
>>> -
>>> - rcu_read_unlock_sched();
>>> -
>>> - if (overflow)
>>> - return notifier_from_errno(-EBUSY);
>>> - }
>>> + set_cpu_active((long)hcpu, false);
>>> return NOTIFY_OK;
>>> + default:
>>> + return NOTIFY_DONE;
>>> }
>>> -
>>> - return NOTIFY_DONE;
>>> }
>>>
>>> static int __init migration_init(void)
>>> @@ -7001,7 +6978,6 @@ static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
>>> */
>>>
>>> case CPU_ONLINE:
>>> - case CPU_DOWN_FAILED:
>>> cpuset_update_active_cpus(true);
>>> break;
>>> default:
>>> @@ -7013,8 +6989,32 @@ static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
>>> static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
>>> void *hcpu)
>>> {
>>> - switch (action) {
>>> + unsigned long flags;
>>> + long cpu = (long)hcpu;
>>> + struct dl_bw *dl_b;
>>> +
>>> + switch (action & ~CPU_TASKS_FROZEN) {
>>> case CPU_DOWN_PREPARE:
>>> + /* explicitly allow suspend */
>>> + if (!(action & CPU_TASKS_FROZEN)) {
>>> + bool overflow;
>>> + int cpus;
>>> +
>>> + rcu_read_lock_sched();
>>> + dl_b = dl_bw_of(cpu);
>>> +
>>> + raw_spin_lock_irqsave(&dl_b->lock, flags);
>>> + cpus = dl_bw_cpus(cpu);
>>> + overflow = __dl_overflow(dl_b, cpus, 0, 0);
>>> + raw_spin_unlock_irqrestore(&dl_b->lock, flags);
>>> +
>>> + rcu_read_unlock_sched();
>>> +
>>> + if (overflow) {
>>> + trace_printk("hotplug failed for cpu %lu", cpu);
>>> + return notifier_from_errno(-EBUSY);
>>> + }
>>> + }
>>> cpuset_update_active_cpus(false);
>>> break;
>>> case CPU_DOWN_PREPARE_FROZEN:
>>> --
>>> 2.3.0
>>
--
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