Re: [PATCH 1/2] sched: Optimize build_sched_domains() for saving first SD node for a cpu

[Michael Wang <wangyun@linux.vnet.ibm.com>]

Hi, Viresh

On 06/04/2013 07:20 PM, Viresh Kumar wrote:
[snip]
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 58453b8..638f6cb 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6533,16 +6533,13 @@ static int build_sched_domains(const struct cpumask *cpu_map,
>  		sd = NULL;
>  		for (tl = sched_domain_topology; tl->init; tl++) {
>  			sd = build_sched_domain(tl, &d, cpu_map, attr, sd, i);
> +			if (!*per_cpu_ptr(d.sd, i))

What about:
			if (tl == sched_domain_topology)

It cost less than per_cpu_ptr(), isn't it?

Regards,
Michael Wang

> +				*per_cpu_ptr(d.sd, i) = sd;
>  			if (tl->flags & SDTL_OVERLAP || sched_feat(FORCE_SD_OVERLAP))
>  				sd->flags |= SD_OVERLAP;
>  			if (cpumask_equal(cpu_map, sched_domain_span(sd)))
>  				break;
>  		}
> -
> -		while (sd->child)
> -			sd = sd->child;
> -
> -		*per_cpu_ptr(d.sd, i) = sd;
>  	}
> 
>  	/* Build the groups for the domains */
>