Re: [sched] 143e1e28cb4: +17.9% aim7.jobs-per-min, -9.7% hackbench.throughput

[Preeti U Murthy <preeti@linux.vnet.ibm.com>]

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On 08/11/2014 07:03 PM, Peter Zijlstra wrote:
> 
> Now I think I see why this is; we've reduced load balancing frequency
> significantly on this machine due to:

We have also changed the value of busy_factor to 32 from 64 across all
domains. This would contribute to increased frequency of load balancing?

Regards
Preeti U Murthy
> 
> 
> -#define SD_SIBLING_INIT (struct sched_domain) {                                \
> -       .min_interval           = 1,                                    \
> -       .max_interval           = 2,                                    \
> 
> 
> -#define SD_MC_INIT (struct sched_domain) {                             \
> -       .min_interval           = 1,                                    \
> -       .max_interval           = 4,                                    \
> 
> 
> -#define SD_CPU_INIT (struct sched_domain) {                            \
> -       .min_interval           = 1,                                    \
> -       .max_interval           = 4,                                    \
> 
> 
>         *sd = (struct sched_domain){
>                 .min_interval           = sd_weight,
>                 .max_interval           = 2*sd_weight,
> 
> Which both increased the min and max value significantly for all domains
> involved.
> 
> That said; I think we might want to do something like the below; I can
> imagine decreasing load balancing too much will negatively impact other
> workloads.
> 
> Maybe slightly modified to make sure the first domain has a min_interval
> of 1.
> 
> ---
>  kernel/sched/core.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1211575a2208..67ed5d854da1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6049,8 +6049,8 @@ sd_init(struct sched_domain_topology_level *tl, int cpu)
>  		sd_flags &= ~TOPOLOGY_SD_FLAGS;
>  
>  	*sd = (struct sched_domain){
> -		.min_interval		= sd_weight,
> -		.max_interval		= 2*sd_weight,
> +		.min_interval		= max(1, sd_weight/2),
> +		.max_interval		= sd_weight,
>  		.busy_factor		= 32,
>  		.imbalance_pct		= 125,
>  
> @@ -6076,7 +6076,7 @@ sd_init(struct sched_domain_topology_level *tl, int cpu)
>  					,
>  
>  		.last_balance		= jiffies,
> -		.balance_interval	= sd_weight,
> +		.balance_interval	= max(1, sd_weight/2),
>  		.smt_gain		= 0,
>  		.max_newidle_lb_cost	= 0,
>  		.next_decay_max_lb_cost	= jiffies,
>