diff mbox

[RFC,4/7] sched: Replace sd_busy/nr_busy_cpus with sched_domain_shared

Message ID 5739E7BC.70205@arm.com
State New
Headers show

Commit Message

Dietmar Eggemann May 16, 2016, 3:31 p.m. UTC 
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);

Comments

Dietmar Eggemann May 16, 2016, 5:26 p.m. UTC | #1 
On 16/05/16 18:02, Peter Zijlstra wrote:
> On Mon, May 16, 2016 at 04:31:08PM +0100, Dietmar Eggemann wrote:

>> 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?

> 

> Sure; but why would I want to add that extra dereference? Note that in

> the next patch I add more users of sd_llc_shared.

> 


I see ... I thought because you do this already in
set_cpu_sd_state_[busy|idle]. But there you need the sd reference to set
sd->nohz_idle already.
diff mbox

Patch

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;