Re: [PATCH] sched/rt: fix rt runtime corrupt when dl refuse a smaller bandwidth

Wanpeng Li
2014-11-18T22:42:09Z

Hi Juri,
On Tue, Nov 18, 2014 at 06:00:20PM +0000, Juri Lelli wrote:
>Hi,
>
>On 13/11/14 08:47, Wanpeng Li wrote:
>> Dl class will refuse the bandwidth being set to some value smaller
>> than the currently allocated bandwidth in any of the root_domains
>> through sched_rt_runtime_us and sched_rt_period_us. RT runtime will
>> be set according to sched_rt_runtime_us before dl class verify if
>> the new bandwidth is suitable in the case of !CONFIG_RT_GROUP_SCHED.
>>
>> However, rt runtime will be corrupt if dl refuse the new bandwidth
>> since there is no undo to reset the rt runtime to the old value.
>>
>
>Can't we just move sched_dl_global_constraints() before
>sched_rt_global_constraints(), and change the name of the
>former to sched_dl_global_validate() ?

Good idea, I will send out the next version later. ;-)

Regards,
Wanpeng Li

>
>Thanks,
>
>- Juri
>
>> This patch fix it by setting rt runtime after all kinds of rational
>> checking in the case of !CONFIG_RT_GROUP_SCHED.
>>
>> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
>> ---
>> kernel/sched/core.c | 30 ++++++++++++++++--------------
>> 1 file changed, 16 insertions(+), 14 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 2e7578a..355dde3 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -7795,20 +7795,7 @@ static int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)
>> #else /* !CONFIG_RT_GROUP_SCHED */
>> static int sched_rt_global_constraints(void)
>> {
>> - unsigned long flags;
>> - int i, ret = 0;
>> -
>> - raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
>> - for_each_possible_cpu(i) {
>> - struct rt_rq *rt_rq = &cpu_rq(i)->rt;
>> -
>> - raw_spin_lock(&rt_rq->rt_runtime_lock);
>> - rt_rq->rt_runtime = global_rt_runtime();
>> - raw_spin_unlock(&rt_rq->rt_runtime_lock);
>> - }
>> - raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
>> -
>> - return ret;
>> + return 0;
>> }
>> #endif /* CONFIG_RT_GROUP_SCHED */
>>
>> @@ -7890,6 +7877,21 @@ static int sched_rt_global_validate(void)
>>
>> static void sched_rt_do_global(void)
>> {
>> +#ifndef CONFIG_RT_GROUP_SCHED
>> + unsigned long flags;
>> + int i;
>> +
>> + raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
>> + for_each_possible_cpu(i) {
>> + struct rt_rq *rt_rq = &cpu_rq(i)->rt;
>> +
>> + raw_spin_lock(&rt_rq->rt_runtime_lock);
>> + rt_rq->rt_runtime = global_rt_runtime();
>> + raw_spin_unlock(&rt_rq->rt_runtime_lock);
>> + }
>> + raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
>> +#endif
>> +
>> def_rt_bandwidth.rt_runtime = global_rt_runtime();
>> def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
>> }
>>