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

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Date:	Wed, 5 Jun 2013 13:04:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Michael Wang <wangyun@...ux.vnet.ibm.com>, mingo@...hat.com,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	linux-kernel@...r.kernel.org, robin.randhawa@....com,
	Steve.Bannister@....com, Liviu.Dudau@....com,
	charles.garcia-tobin@....com, arvind.chauhan@....com
Subject: Re: [PATCH 1/2] sched: Optimize build_sched_domains() for saving
 first SD node for a cpu

On Wed, Jun 05, 2013 at 10:37:29AM +0530, Viresh Kumar wrote:
> On 5 June 2013 10:12, Michael Wang <wangyun@...ux.vnet.ibm.com> wrote:
> > 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?
> 
> How can I miss it.. Obviously its better :)
> 
> See if below one looks better (Attached too in case gmail screws up
> my mail)..
> 
> --------x-------------x------------------
> 
> From: Viresh Kumar <viresh.kumar@...aro.org>
> Date: Tue, 4 Jun 2013 15:41:15 +0530
> Subject: [PATCH] sched: Optimize build_sched_domains() for saving first SD
>  node for a cpu
> 
> We are saving first scheduling domain for a cpu in build_sched_domains() by
> iterating over the nested sd->child list. We don't actually need to do it this
> way.
> 
> tl will be equal to sched_domain_topology for the first iteration and so we can
> set *per_cpu_ptr(d.sd, i) based on that.  So, save pointer to first SD while
> running the iteration loop over tl's.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  kernel/sched/core.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 58453b8..08a27be 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,

Applying patch
patches/viresh_kumar-_patch__sched-optimize_build_sched_domains_for_saving_first_sd.patch
patching file kernel/sched/core.c
patch: **** malformed patch at line 56: cpumask *cpu_map,

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