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Subject[patch 6/7] sched: change nohz.load_balancer to be nr_cpu_ids based
From: Venkatesh Pallipadi <venki@google.com>
Subject: sched: change nohz.load_balancer to be nr_cpu_ids based

nohz.load_balancer was using -1 when it is not set to any cpu. Change it
to nr_cpu_ids, making it similar to other such variables in this file.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
kernel/hrtimer.c | 2 +-
kernel/sched.c | 1 +
kernel/sched_fair.c | 26 ++++++++++++++++----------
kernel/timer.c | 2 +-
4 files changed, 19 insertions(+), 12 deletions(-)
Index: tip/kernel/sched_fair.c
===================================================================
--- tip.orig/kernel/sched_fair.c
+++ tip/kernel/sched_fair.c
@@ -3101,13 +3101,15 @@ static struct {
cpumask_var_t idle_cpus_mask;
cpumask_var_t grp_idle_mask;
unsigned long next_balance; /* in jiffy units */
-} nohz ____cacheline_aligned = {
- .load_balancer = ATOMIC_INIT(-1),
-};
+} nohz ____cacheline_aligned;

int get_nohz_load_balancer(void)
{
- return atomic_read(&nohz.load_balancer);
+ int load_balancer = atomic_read(&nohz.load_balancer);
+ if (load_balancer >= nr_cpu_ids)
+ return nr_cpu_ids;
+
+ return load_balancer;
}

#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
@@ -3237,7 +3239,8 @@ static void nohz_balancer_kick(int cpu)
nohz.next_balance++;

ilb_cpu = get_nohz_load_balancer();
- if (ilb_cpu < 0) {
+
+ if (ilb_cpu >= nr_cpu_ids) {
ilb_cpu = cpumask_first(nohz.idle_cpus_mask);
if (ilb_cpu >= nr_cpu_ids)
return;
@@ -3279,7 +3282,8 @@ void select_nohz_load_balancer(int stop_
* If we are going offline and still the leader,
* give up!
*/
- if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
+ if (atomic_cmpxchg(&nohz.load_balancer, cpu,
+ nr_cpu_ids) != cpu)
BUG();

return;
@@ -3292,11 +3296,12 @@ void select_nohz_load_balancer(int stop_
if (atomic_read(&nohz.second_pick_cpu) == cpu)
atomic_cmpxchg(&nohz.second_pick_cpu, cpu, nr_cpu_ids);

- if (atomic_read(&nohz.load_balancer) == -1) {
+ if (atomic_read(&nohz.load_balancer) >= nr_cpu_ids) {
int new_ilb;

/* make me the ilb owner */
- if (atomic_cmpxchg(&nohz.load_balancer, -1, cpu) != -1)
+ if (atomic_cmpxchg(&nohz.load_balancer, nr_cpu_ids,
+ cpu) != nr_cpu_ids)
return;

/*
@@ -3305,7 +3310,7 @@ void select_nohz_load_balancer(int stop_
*/
new_ilb = find_new_ilb(cpu);
if (new_ilb < nr_cpu_ids && new_ilb != cpu) {
- atomic_set(&nohz.load_balancer, -1);
+ atomic_set(&nohz.load_balancer, nr_cpu_ids);
resched_cpu(new_ilb);
return;
}
@@ -3318,7 +3323,8 @@ void select_nohz_load_balancer(int stop_
cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);

if (atomic_read(&nohz.load_balancer) == cpu)
- if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
+ if (atomic_cmpxchg(&nohz.load_balancer, cpu,
+ nr_cpu_ids) != cpu)
BUG();
}
return;
Index: tip/kernel/sched.c
===================================================================
--- tip.orig/kernel/sched.c
+++ tip/kernel/sched.c
@@ -7656,6 +7656,7 @@ void __init sched_init(void)
#ifdef CONFIG_NO_HZ
zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
alloc_cpumask_var(&nohz.grp_idle_mask, GFP_NOWAIT);
+ atomic_set(&nohz.load_balancer, nr_cpu_ids);
atomic_set(&nohz.first_pick_cpu, nr_cpu_ids);
atomic_set(&nohz.second_pick_cpu, nr_cpu_ids);
#endif
Index: tip/kernel/hrtimer.c
===================================================================
--- tip.orig/kernel/hrtimer.c
+++ tip/kernel/hrtimer.c
@@ -147,7 +147,7 @@ static int hrtimer_get_target(int this_c
if (!pinned && get_sysctl_timer_migration() && idle_cpu(this_cpu)) {
int preferred_cpu = get_nohz_load_balancer();

- if (preferred_cpu >= 0)
+ if (preferred_cpu < nr_cpu_ids)
return preferred_cpu;
}
#endif
Index: tip/kernel/timer.c
===================================================================
--- tip.orig/kernel/timer.c
+++ tip/kernel/timer.c
@@ -682,7 +682,7 @@ __mod_timer(struct timer_list *timer, un
if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu)) {
int preferred_cpu = get_nohz_load_balancer();

- if (preferred_cpu >= 0)
+ if (preferred_cpu < nr_cpu_ids)
cpu = preferred_cpu;
}
#endif



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