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

[Vincent Guittot]

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:

...

> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -8215,12 +8215,8 @@ group_has_capacity(unsigned int imbalanc
> >   	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))
> > +	if ((sgs->group_capacity * 100) > (sgs->group_util * imbalance_pct) &&
> > +	    (sgs->group_capacity * 100) > (sgs->group_runnable * imbalance_pct))
> >   		return true;
> >   	return false;
> > @@ -8240,12 +8236,8 @@ group_is_overloaded(unsigned int imbalan
> >   	if (sgs->sum_nr_running <= sgs->group_weight)
> >   		return false;
> > -	if ((sgs->group_capacity * 100) <
> > -			(sgs->group_util * imbalance_pct))
> > -		return true;
> > -
> > -	if ((sgs->group_capacity * imbalance_pct) <
> > -			(sgs->group_runnable * 100))
> > +	if ((sgs->group_capacity * 100) < (sgs->group_util * imbalance_pct) ||
> > +	    (sgs->group_capacity * 100) < (sgs->group_runnable * imbalance_pct))
> >   		return true;
> >   	return false;
> > 
> 
> I apply the patch based on v5.7, the regression still existed.

Thanks for the test. I don't know if it's relevant or not but the results seem a bit
better with the patch and I'd like to check that it's only a matter of threshold to
fix the problem.

Could you try the patch below which is quite aggressive but will help to confirm this ?

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 28be1c984a42..3c51d557547b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8322,10 +8322,13 @@ static inline int sg_imbalanced(struct sched_group *group)
 static inline bool
 group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 {
+       unsigned long imb;
+
        if (sgs->sum_nr_running < sgs->group_weight)
                return true;

-       if ((sgs->group_capacity * imbalance_pct) <
+       imb = sgs->sum_nr_running * 100;
+       if ((sgs->group_capacity * imb) <
                        (sgs->group_runnable * 100))
                return false;

@@ -8347,6 +8350,8 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 static inline bool
 group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 {
+       unsigned long imb;
+
        if (sgs->sum_nr_running <= sgs->group_weight)
                return false;

@@ -8354,7 +8359,8 @@ 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) <
+       imb = sgs->sum_nr_running * 100;
+       if ((sgs->group_capacity * imb) <
                        (sgs->group_runnable * 100))
                return true;


> 
> =========================================================================================
> 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
>   6b33257768b8dd3982054885ea310871be2cfe0b (Hillf's patch)
> 
> 9f68395333ad7f5b 070f5e860ee2bf588c99ef7b4c2                        v5.7
> 6b33257768b8dd3982054885ea3
> ---------------- --------------------------- ---------------------------
> ---------------------------
>          %stddev     %change         %stddev     %change %stddev     %change
> %stddev
>              \          |                \          |                \
> |                \
>       0.69           -10.3%       0.62            -9.1%       0.62
> -10.1%       0.62        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
> -8.3%      61305        reaim.jobs_per_min
>      16717           -10.0%      15046            -7.6%      15446
> -8.3%      15326        reaim.jobs_per_min_child
>      97.84            -1.1%      96.75            -0.4%      97.43
> -0.5%      97.37        reaim.jti
>      72000           -10.8%      64216            -8.3%      66000
> -8.3%      66000        reaim.max_jobs_per_min
>       0.36           +10.6%       0.40            +7.8%       0.39
> +9.4%       0.39        reaim.parent_time
>       1.58 ±  2%     +71.0%       2.70 ±  2%     +26.9%       2.01 ± 2%
> +33.2%       2.11        reaim.std_dev_percent
>       0.00 ±  5%    +110.4%       0.01 ±  3%     +48.8%       0.01 ± 7%
> +65.3%       0.01 ±  3%  reaim.std_dev_time
>      50800            -2.4%      49600            -1.6%      50000
> -1.8%      49866        reaim.workload
> 
> 
> 
> -- 
> Zhengjun Xing