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

Xing Zhengjun
2020-06-19T05:01:38Z

On 6/18/2020 8:35 PM, Vincent Guittot wrote:
> On Thu, 18 Jun 2020 at 04:45, Xing Zhengjun
> <zhengjun.xing@linux.intel.com> wrote:
>>
>>
>>
>
>>>>
>>>> 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) {
>>>> /*
>>>> --
>>>> 2.17.1
>>>>
>>>
>>> The patch above tries to move back to the group in the same classification as
>>> before but this could harm other benchmarks.
>>>
>>> There is another way to fix this by easing the migration of task in the case
>>> of migrate_util imbalance.
>>>
>>> Could you also try the patch below instead of the one above ?
>>>
>>> ---
>>> kernel/sched/fair.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index 0aeffff62807..fcaf66c4d086 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -7753,7 +7753,8 @@ static int detach_tasks(struct lb_env *env)
>>> case migrate_util:
>>> util = task_util_est(p);
>>>
>>> - if (util > env->imbalance)
>>> + if (util/2 > env->imbalance &&
>>> + env->sd->nr_balance_failed <= env->sd->cache_nice_tries)
>>> goto next;
>>>
>>> env->imbalance -= util;
>>> --
>>> 2.17.1
>>>
>>>
>>
>> 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
>> 69c81543653bf5f2c7105086502889fa019c15cb (the test patch)
>>
>> 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2 v5.7
>> 69c81543653bf5f2c7105086502
>> ---------------- --------------------------- ---------------------------
>> ---------------------------
>> %stddev %change %stddev %change
>> %stddev %change %stddev
>> \ | \ | \
>> | \
>> 0.69 -10.3% 0.62 -9.1% 0.62
>> -7.6% 0.63 reaim.child_systime
>> 0.62 -1.0% 0.61 +0.5% 0.62
>> +1.9% 0.63 reaim.child_utime
>> 66870 -10.0% 60187 -7.6% 61787
>> -5.9% 62947 reaim.jobs_per_min
>
> There is an improvement but not at the same level as on my setup.
> I'm not sure with patch you tested here. Is it the last one that
> modify detach_tasks() or the previous one that modify
> post_init_entity_util_avg() ?
>
It is the last one that modify detach_tasks().

> Could you also try the other one ? Both patches were improving results
> on y setup but the behavior doesn't seem to be the same on your setup.
>

The test result for the other one has been sent in another mail.

>
>> 16717 -10.0% 15046 -7.6% 15446
>> -5.9% 15736 reaim.jobs_per_min_child
>> 97.84 -1.1% 96.75 -0.4% 97.43
>> -0.4% 97.47 reaim.jti
>> 72000 -10.8% 64216 -8.3% 66000
>> -5.7% 67885 reaim.max_jobs_per_min
>> 0.36 +10.6% 0.40 +7.8% 0.39
>> +6.0% 0.38 reaim.parent_time
>> 1.58 ± 2% +71.0% 2.70 ± 2% +26.9% 2.01 ±
>> 2% +23.6% 1.95 ± 3% reaim.std_dev_percent
>> 0.00 ± 5% +110.4% 0.01 ± 3% +48.8% 0.01 ±
>> 7% +43.2% 0.01 ± 5% reaim.std_dev_time
>> 50800 -2.4% 49600 -1.6% 50000
>> -0.8% 50400 reaim.workload
>>
>>
>>>>
>>>>
> ...
>>>>>>>
>>>>>>> --
>>>>>>> Zhengjun Xing
>>>>>
>>>>> --
>>>>> Zhengjun Xing
>>
>> --
>> Zhengjun Xing

--
Zhengjun Xing