On 06/05/2013 01:07 PM, Viresh Kumar wrote:
> On 5 June 2013 10:12, Michael Wang <wang...@linux.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)..
Looks good to me :)
Regards,
Michael Wang
>
> --------x-------------x------------------
>
> From: Viresh Kumar <viresh.ku...@linaro.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.ku...@linaro.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,
> sd = NULL;
> for (tl = sched_domain_topology; tl->init; tl++) {
> sd = build_sched_domain(tl, &d, cpu_map, attr, sd, i);
> + if (tl == sched_domain_topology)
> + *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 */
>
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