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Subject[PATCH 1/2] [RESEND] sched: Fully integrate cpus_active_map and root-domain code
Date
(Applies to 2.6.31-rc4)

[
This patch was originaly sent about a year ago, but got dropped
presumably by accident. Here is the original thread.

http://lkml.org/lkml/2008/7/22/281

At that time, Peter and Max acked it. It has now been forward
ported to the new cpumask interface. I will be so bold as to
carry their acks forward since the basic logic is the same.
However, a new acknowledgement, if they have the time to review,
would be ideal.

I have tested this patch on a 4-way system using Max's recommended
"echo 0|1 > cpu1/online" technique and it appears to work properly
]

What: Reflect "active" cpus in the rq->rd->online field, instead of the
online_map.

Motivation: Things that use the root-domain code (such as cpupri) only
care about cpus classified as "active" anyway. By synchronizing the
root-domain state with the active map, we allow several optimizations.

For instance, we can remove an extra cpumask_and from the scheduler
hotpath by utilizing rq->rd->online (since it is now a cached version
of cpu_active_map & rq->rd->span).

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Max Krasnyansky <maxk@qualcomm.com>
---

kernel/sched.c | 2 +-
kernel/sched_fair.c | 10 +++++++---
kernel/sched_rt.c | 7 -------
3 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 1a104e6..38a1526 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7874,7 +7874,7 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
rq->rd = rd;

cpumask_set_cpu(rq->cpu, rd->span);
- if (cpumask_test_cpu(rq->cpu, cpu_online_mask))
+ if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
set_rq_online(rq);

spin_unlock_irqrestore(&rq->lock, flags);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 9ffb2b2..2b9cae6 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1040,17 +1040,21 @@ static void yield_task_fair(struct rq *rq)
* search starts with cpus closest then further out as needed,
* so we always favor a closer, idle cpu.
* Domains may include CPUs that are not usable for migration,
- * hence we need to mask them out (cpu_active_mask)
+ * hence we need to mask them out (rq->rd->online)
*
* Returns the CPU we should wake onto.
*/
#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
+
+#define cpu_rd_active(cpu, rq) cpumask_test_cpu(cpu, rq->rd->online)
+
static int wake_idle(int cpu, struct task_struct *p)
{
struct sched_domain *sd;
int i;
unsigned int chosen_wakeup_cpu;
int this_cpu;
+ struct rq *task_rq = task_rq(p);

/*
* At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu
@@ -1083,10 +1087,10 @@ static int wake_idle(int cpu, struct task_struct *p)
for_each_domain(cpu, sd) {
if ((sd->flags & SD_WAKE_IDLE)
|| ((sd->flags & SD_WAKE_IDLE_FAR)
- && !task_hot(p, task_rq(p)->clock, sd))) {
+ && !task_hot(p, task_rq->clock, sd))) {
for_each_cpu_and(i, sched_domain_span(sd),
&p->cpus_allowed) {
- if (cpu_active(i) && idle_cpu(i)) {
+ if (cpu_rd_active(i, task_rq) && idle_cpu(i)) {
if (i != task_cpu(p)) {
schedstat_inc(p,
se.nr_wakeups_idle);
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index a8f89bc..13f728e 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1173,13 +1173,6 @@ static int find_lowest_rq(struct task_struct *task)
return -1; /* No targets found */

/*
- * Only consider CPUs that are usable for migration.
- * I guess we might want to change cpupri_find() to ignore those
- * in the first place.
- */
- cpumask_and(lowest_mask, lowest_mask, cpu_active_mask);
-
- /*
* At this point we have built a mask of cpus representing the
* lowest priority tasks in the system. Now we want to elect
* the best one based on our affinity and topology.


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