On Tue, Jul 23, 2013 at 09:44:17PM +0600, Rakib Mullick wrote:
> Currently, update_top_cache_domain() is called whenever schedule domain is
> built or destroyed. But, the following
> callpath shows that they're at the same callpath and can be avoided
> update_top_cache_domain() while destroying schedule
> domain and update only at the times of building schedule domains.
>
> partition_sched_domains()
> detach_destroy_domain()
> cpu_attach_domain()
> update_top_cache_domain()
> build_sched_domains()
> cpu_attach_domain()
> update_top_cache_domain()
>
Does it really matter?
>
> Signed-off-by: Rakib Mullick <rakib.mull...@gmail.com>
> ---
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b7c32cb..8c6fee4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5102,8 +5102,8 @@ static void update_top_cache_domain(int cpu)
> * Attach the domain 'sd' to 'cpu' as its base domain. Callers must
> * hold the hotplug lock.
> */
> -static void
> -cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
> +static void cpu_attach_domain(struct sched_domain *sd, struct root_domain
> *rd,
> + int cpu, bool update_cache_domain)
> {
> struct rq *rq = cpu_rq(cpu);
> struct sched_domain *tmp;
> @@ -5138,7 +5138,8 @@ cpu_attach_domain(struct sched_domain *sd, struct
> root_domain *rd, int cpu)
> rcu_assign_pointer(rq->sd, sd);
> destroy_sched_domains(tmp, cpu);
>
> - update_top_cache_domain(cpu);
> + if (update_cache_domain)
> + update_top_cache_domain(cpu);
> }
>
> /* cpus with isolated domains */
> @@ -6021,7 +6022,7 @@ static int build_sched_domains(const struct cpumask
> *cpu_map,
> rcu_read_lock();
> for_each_cpu(i, cpu_map) {
> sd = *per_cpu_ptr(d.sd, i);
> - cpu_attach_domain(sd, d.rd, i);
> + cpu_attach_domain(sd, d.rd, i, 1);
> }
> rcu_read_unlock();
>
> @@ -6109,7 +6110,7 @@ static void detach_destroy_domains(const struct cpumask
> *cpu_map)
>
> rcu_read_lock();
> for_each_cpu(i, cpu_map)
> - cpu_attach_domain(NULL, &def_root_domain, i);
> + cpu_attach_domain(NULL, &def_root_domain, i, 0);
> rcu_read_unlock();
> }
This just makes the code uglier for no gain afaict.
If you really need to do this, key off @sd == NULL or something.
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