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sched: fix idle load balancing in softirqd context

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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.

[kernel@kolivas.org: Fix reverse idle at tick logic]
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Siddha, Suresh B 2007-05-08 00:32:48 -07:00 committed by Linus Torvalds
parent 2bd7e20e0d
commit bdecea3a92
1 changed files with 5 additions and 7 deletions
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12
kernel/sched.c
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@ -223,6 +223,7 @@ 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;
@ -2943,12 +2944,7 @@ static void run_rebalance_domains(struct softirq_action *h)
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;
@ -3218,14 +3214,16 @@ void scheduler_tick(void)
unsigned long long now = sched_clock();
struct task_struct *p = current;
int cpu = smp_processor_id();
int idle_at_tick = idle_cpu(cpu);
struct rq *rq = cpu_rq(cpu);
update_cpu_clock(p, rq, now);
if (p != rq->idle)
if (!idle_at_tick)
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