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

Xing Zhengjun
2020-06-19T04:56:03Z

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