Periodic load balancing in recent kernels happen in the softirq.
In certain -rt configurations, these softirqs are handled in softirqd
context. And hence the check for idle processor was always returning
busy (as nr_running > 1).
This patch captures the idle information at the tick and passes this info
to softirq context through an element 'idle_at_tick' in rq.
Signed-off-by: Suresh Siddha <[email protected]>
---
diff -pNru linux-2.6.20.x86_64/kernel/sched.c linux/kernel/sched.c
--- linux-2.6.20.x86_64/kernel/sched.c 2007-02-10 03:41:27.000000000 -0800
+++ linux/kernel/sched.c 2007-02-16 16:22:44.000000000 -0800
@@ -240,6 +240,7 @@ struct rq {
unsigned long raw_weighted_load;
#ifdef CONFIG_SMP
unsigned long cpu_load[3];
+ unsigned char idle_at_tick;
#endif
unsigned long long nr_switches;
@@ -3350,12 +3351,7 @@ static void run_rebalance_domains(struct
struct rq *this_rq = cpu_rq(this_cpu);
unsigned long interval;
struct sched_domain *sd;
- /*
- * We are idle if there are no processes running. This
- * is valid even if we are the idle process (SMT).
- */
- enum idle_type idle = !this_rq->nr_running ?
- SCHED_IDLE : NOT_IDLE;
+ enum idle_type idle = this_rq->idle_at_tick ? SCHED_IDLE : NOT_IDLE;
/* Earliest time when we have to call run_rebalance_domains again */
unsigned long next_balance = jiffies + 60*HZ;
@@ -3651,20 +3647,21 @@ void scheduler_tick(void)
{
unsigned long long now = sched_clock();
struct task_struct *p = current;
- int cpu = smp_processor_id();
+ int cpu = smp_processor_id(), idle_at_tick = idle_cpu(cpu);
struct rq *rq = cpu_rq(cpu);
BUG_ON(!irqs_disabled());
update_cpu_clock(p, rq, now);
- if (p == rq->idle)
+ if (idle_at_tick)
/* Task on the idle queue */
wake_priority_sleeper(rq);
else
task_running_tick(rq, p);
#ifdef CONFIG_SMP
update_load(rq);
+ rq->idle_at_tick = idle_at_tick;
if (time_after_eq(jiffies, rq->next_balance))
raise_softirq(SCHED_SOFTIRQ);
#endif
-
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