Re: [LKP] [sched/fair] 070f5e860e: reaim.jobs_per_min -10.5% regression

[Xing Zhengjun <zhengjun.xing@linux.intel.com>]

On 6/17/2020 10:57 PM, Vincent Guittot wrote:
> Le mercredi 17 juin 2020 à 08:30:21 (+0800), Xing Zhengjun a écrit :
>>
>>
>> On 6/16/2020 2:54 PM, Vincent Guittot wrote:
>>>
>>> Hi Xing,
>>>
>>> Le mardi 16 juin 2020 à 11:17:16 (+0800), Xing Zhengjun a écrit :
>>>>
>>>>
>>>> On 6/15/2020 4:10 PM, Vincent Guittot wrote:
>>>>> Hi Xing,
>>>>>
>>>>> Le lundi 15 juin 2020 à 15:26:59 (+0800), Xing Zhengjun a écrit :
>>>>>>
>>>>>>
>>>>>> On 6/12/2020 7:06 PM, Hillf Danton wrote:
>>>>>>>
>>>>>>> On Fri, 12 Jun 2020 14:36:49 +0800 Xing Zhengjun wrote:
>>>>>
>>>
>>> ...
>>>
>>>>>
>>>>
>>>> I apply the patch based on v5.7, the test result is as the following:
>>>
>>> TBH, I didn't expect that the results would still be bad, so i wonder if the threshold are
>>> the root problem.
>>>
>>> Could you run tests with the patch below that removes condition with runnable_avg ?
>>> I just want to make sure that those 2 conditions are the root cause.
>>>
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index da3e5b54715b..f5774d0af059 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -8210,10 +8210,6 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
>>>           if (sgs->sum_nr_running < sgs->group_weight)
>>>                   return true;
>>>
>>> -       if ((sgs->group_capacity * imbalance_pct) <
>>> -                       (sgs->group_runnable * 100))
>>> -               return false;
>>> -
>>>           if ((sgs->group_capacity * 100) >
>>>                           (sgs->group_util * imbalance_pct))
>>>                   return true;
>>> @@ -8239,10 +8235,6 @@ group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
>>>                           (sgs->group_util * imbalance_pct))
>>>                   return true;
>>>
>>> -       if ((sgs->group_capacity * imbalance_pct) <
>>> -                       (sgs->group_runnable * 100))
>>> -               return true;
>>> -
>>>           return false;
>>>    }
>>>
>>>
>>>
>>> Thanks.
>>> Vincent
>>>
>>
>>
>> I apply the patch based on v5.7, the test result is as the following:
>>
>> =========================================================================================
>> tbox_group/testcase/rootfs/kconfig/compiler/runtime/nr_task/debug-setup/test/cpufreq_governor/ucode:
>>
>> lkp-ivb-d04/reaim/debian-x86_64-20191114.cgz/x86_64-rhel-7.6/gcc-7/300s/100%/test/five_sec/performance/0x21
>>
>> commit:
>>    9f68395333ad7f5bfe2f83473fed363d4229f11c
>>    070f5e860ee2bf588c99ef7b4c202451faa48236
>>    v5.7
>>    63a5d0fbb5ec62f5148c251c01e709b8358cd0ee (the test patch)
>>
>> 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2                        v5.7
>> 63a5d0fbb5ec62f5148c251c01e
>> ---------------- --------------------------- ---------------------------
>> ---------------------------
>>           %stddev     %change         %stddev     %change %stddev     %change
>> %stddev
>>               \          |                \          |                \
>> |                \
>>        0.69           -10.3%       0.62            -9.1%       0.62
>> +1.0%       0.69        reaim.child_systime
>>        0.62            -1.0%       0.61            +0.5%       0.62
>> -0.1%       0.62        reaim.child_utime
>>       66870           -10.0%      60187            -7.6%      61787
>> +1.1%      67636        reaim.jobs_per_min
>>       16717           -10.0%      15046            -7.6%      15446
>> +1.1%      16909        reaim.jobs_per_min_child
> 
> OK. So the regression disappears when the conditions on runnable_avg are removed.
> 
> In the meantime, I have been able to understand more deeply what was happeningi
> for this bench and how it is impacted by
>    commit: 070f5e860ee2 ("sched/fair: Take into account runnable_avg to classify group")
> 
> This bench forks a new thread for each and every new step. But a newly forked
> threads start with a load_avg and a runnable_avg set to max whereas the threads
> are running shortly before exiting. This makes the CPU to be set overloaded in
> some case whereas it isn't.
> 
> Could you try the patch below ?
> It fixes the problem on my setup (I have finally been able to reproduce the problem)
> 
> ---
>   kernel/sched/fair.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0aeffff62807..b33a4a9e1491 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -807,7 +807,7 @@ void post_init_entity_util_avg(struct task_struct *p)
>   		}
>   	}
>   
> -	sa->runnable_avg = cpu_scale;
> +	sa->runnable_avg = sa->util_avg;
>   
>   	if (p->sched_class != &fair_sched_class) {
>   		/*
> 

I apply the patch above based on v5.7, the test result is as the following:

=========================================================================================
tbox_group/testcase/rootfs/kconfig/compiler/runtime/nr_task/debug-setup/test/cpufreq_governor/ucode:
 
lkp-ivb-d04/reaim/debian-x86_64-20191114.cgz/x86_64-rhel-7.6/gcc-7/300s/100%/test/five_sec/performance/0x21

commit:
   9f68395333ad7f5bfe2f83473fed363d4229f11c
   070f5e860ee2bf588c99ef7b4c202451faa48236
   v5.7
   cbb4d668e7431479a7978fa79d64c2271adefab0 ( the test patch which modify
post_init_entity_util_avg())

9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2                        v5.7 
cbb4d668e7431479a7978fa79d6
---------------- --------------------------- --------------------------- 
---------------------------
          %stddev     %change         %stddev     %change 
%stddev     %change         %stddev
              \          |                \          |                \ 
         |                \
       0.69           -10.3%       0.62            -9.1%       0.62 
       +0.6%       0.69        reaim.child_systime
       0.62            -1.0%       0.61            +0.5%       0.62 
       -0.3%       0.62        reaim.child_utime
      66870           -10.0%      60187            -7.6%      61787 
       +0.7%      67335        reaim.jobs_per_min
      16717           -10.0%      15046            -7.6%      15446 
       +0.7%      16833        reaim.jobs_per_min_child
      97.84            -1.1%      96.75            -0.4%      97.43 
       +0.2%      98.05        reaim.jti
      72000           -10.8%      64216            -8.3%      66000 
       +0.0%      72000        reaim.max_jobs_per_min
       0.36           +10.6%       0.40            +7.8%       0.39 
       -0.6%       0.36        reaim.parent_time
       1.58 ±  2%     +71.0%       2.70 ±  2%     +26.9%       2.01 ± 
2%      -8.8%       1.44 ±  2%  reaim.std_dev_percent
       0.00 ±  5%    +110.4%       0.01 ±  3%     +48.8%       0.01 ± 
7%     -24.6%       0.00 ±  7%  reaim.std_dev_time
      50800            -2.4%      49600            -1.6%      50000 
       +0.0%      50800        reaim.workload


-- 
Zhengjun Xing