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Subject[patch -rt 13/17] sched: cleanup wake_idle power saving
Hopefully a more readable version of the same.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Dinakar Guniguntala <dino@in.ibm.com>
---
kernel/sched_fair.c | 58 ++++++++++++++++++++++++++++++++++------------------
1 file changed, 39 insertions(+), 19 deletions(-)
Index: linux-2.6.31.4-rt14-lb1/kernel/sched_fair.c
===================================================================
--- linux-2.6.31.4-rt14-lb1.orig/kernel/sched_fair.c 2009-10-21 10:47:14.000000000 -0400
+++ linux-2.6.31.4-rt14-lb1/kernel/sched_fair.c 2009-10-21 10:49:01.000000000 -0400
@@ -1040,6 +1040,41 @@
se->vruntime = rightmost->vruntime + 1;
}

+#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
+/*
+ * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu
+ * are idle and this is not a kernel thread and this task's affinity
+ * allows it to be moved to preferred cpu, then just move!
+ *
+ * XXX - can generate significant overload on perferred_wakeup_cpu
+ * with plenty of idle cpus, leading to a significant loss in
+ * throughput.
+ *
+ * Returns: < 0 - no placement decision made
+ * >= 0 - place on cpu
+ */
+static int wake_idle_power_save(int cpu, struct task_struct *p)
+{
+ int this_cpu = smp_processor_id();
+ int wakeup_cpu;
+
+ if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
+ return -1;
+
+ if (!idle_cpu(cpu) || !idle_cpu(this_cpu))
+ return -1;
+
+ if (!p->mm || (p->flags & PF_KTHREAD))
+ return -1;
+
+ wakeup_cpu = cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu;
+
+ if (!cpu_isset(wakeup_cpu, p->cpus_allowed))
+ return -1;
+
+ return wakeup_cpu;
+}
+
/*
* wake_idle() will wake a task on an idle cpu if task->cpu is
* not idle and an idle cpu is available. The span of cpus to
@@ -1050,29 +1085,14 @@
*
* Returns the CPU we should wake onto.
*/
-#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
static int wake_idle(int cpu, struct task_struct *p)
{
struct sched_domain *sd;
int i;
- unsigned int chosen_wakeup_cpu;
- int this_cpu;
-
- /*
- * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu
- * are idle and this is not a kernel thread and this task's affinity
- * allows it to be moved to preferred cpu, then just move!
- */
-
- this_cpu = smp_processor_id();
- chosen_wakeup_cpu =
- cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu;

- if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP &&
- idle_cpu(cpu) && idle_cpu(this_cpu) &&
- p->mm && !(p->flags & PF_KTHREAD) &&
- cpu_isset(chosen_wakeup_cpu, p->cpus_allowed))
- return chosen_wakeup_cpu;
+ i = wake_idle_power_save(cpu, p);
+ if (i >= 0)
+ return i;

/*
* If it is idle, then it is the best cpu to run this task.
@@ -1081,7 +1101,7 @@
* Siblings must be also busy(in most cases) as they didn't already
* pickup the extra load from this cpu and hence we need not check
* sibling runqueue info. This will avoid the checks and cache miss
- * penalities associated with that.
+ * penalties associated with that.
*/
if (idle_cpu(cpu) || cpu_rq(cpu)->cfs.nr_running > 1)
return cpu;
--


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