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SubjectRe: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with sched_domain_shared
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On 09/05/16 11:48, Peter Zijlstra wrote:

Couldn't you just always access sd->shared via
sd = rcu_dereference(per_cpu(sd_llc, cpu)) for
updating nr_busy_cpus?

The call_rcu() thing is on the sd any way.

@@ -5879,7 +5879,6 @@ static void destroy_sched_domains(struct sched_domain *sd)
DEFINE_PER_CPU(struct sched_domain *, sd_llc);
DEFINE_PER_CPU(int, sd_llc_size);
DEFINE_PER_CPU(int, sd_llc_id);
-DEFINE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
DEFINE_PER_CPU(struct sched_domain *, sd_numa);
DEFINE_PER_CPU(struct sched_domain *, sd_asym);

@@ -5900,7 +5899,6 @@ static void update_top_cache_domain(int cpu)
rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
per_cpu(sd_llc_size, cpu) = size;
per_cpu(sd_llc_id, cpu) = id;
- rcu_assign_pointer(per_cpu(sd_llc_shared, cpu), sds);

sd = lowest_flag_domain(cpu, SD_NUMA);
rcu_assign_pointer(per_cpu(sd_numa, cpu), sd);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0d8dad2972b6..5aed6089dae8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8136,7 +8136,6 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
static inline bool nohz_kick_needed(struct rq *rq)
{
unsigned long now = jiffies;
- struct sched_domain_shared *sds;
struct sched_domain *sd;
int nr_busy, cpu = rq->cpu;
bool kick = false;
@@ -8165,13 +8164,13 @@ static inline bool nohz_kick_needed(struct rq *rq)
return true;

rcu_read_lock();
- sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
- if (sds) {
+ sd = rcu_dereference(per_cpu(sd_llc, cpu));
+ if (sd) {
/*
* XXX: write a coherent comment on why we do this.
* See also: http:lkml.kernel.org/r/20111202010832.602203411@sbsiddha-desk.sc.intel.com
*/
- nr_busy = atomic_read(&sds->nr_busy_cpus);
+ nr_busy = atomic_read(&sd->shared->nr_busy_cpus);
if (nr_busy > 1) {
kick = true;
goto unlock;
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