Re: [PATCH] cpu hotplug, sched:Introduce cpu_active_map and redoscheddomainmanagment(take 2)

From: Gregory Haskins
Date: Tue Jul 22 2008 - 10:08:27 EST

Max Krasnyansky wrote:
Greg, correct me if I'm wrong but we seem to have exact same issue with the
rq->rq->online map. Lets take "cpu going down" for example. We're clearing
rq->rd->online bit on DYING event, but nothing AFAICS prevents another cpu
calling rebuild_sched_domains()->partition_sched_domains() in the middle of
the hotplug sequence.
partition_sched_domains() will happily reset rd->rq->online mask and things
will fail. I'm talking about this path

__build_sched_domains() -> cpu_attach_domain() -> rq_attach_root()
cpu_set(rq->cpu, rd->span);
if (cpu_isset(rq->cpu, cpu_online_map))

I think you are right, but wouldn't s/online/active above fix that as well? The active_map didnt exist at the time that code went in initially ;)


btw Why didn't we convert sched*.c to use rq->rd->online when it was
introduced ? ie Instead of using cpu_online_map directly.
I think things were converted where they made sense to convert. But we also had a different goal at that time, so perhaps something was missed. If you think something else should be converted, please point it out.

In the meantime, I would suggest we consider this patch on top of yours (applies to tip/sched/devel):


sched: Fully integrate cpus_active_map and root-domain code
Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx>

diff --git a/kernel/sched.c b/kernel/sched.c
index 62b1b8e..99ba70d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6611,7 +6611,7 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
rq->rd = rd;

cpu_set(rq->cpu, rd->span);
- if (cpu_isset(rq->cpu, cpu_online_map))
+ if (cpu_isset(rq->cpu, cpu_active_map))

spin_unlock_irqrestore(&rq->lock, flags);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 7f70026..2bae8de 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1004,7 +1004,7 @@ 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_map)
+ * hence we need to mask them out (rq->rd->online)
* Returns the CPU we should wake onto.
@@ -1032,7 +1032,7 @@ static int wake_idle(int cpu, struct task_struct *p)
|| ((sd->flags & SD_WAKE_IDLE_FAR)
&& !task_hot(p, task_rq(p)->clock, sd))) {
cpus_and(tmp, sd->span, p->cpus_allowed);
- cpus_and(tmp, tmp, cpu_active_map);
+ cpus_and(tmp, tmp, task_rq(p)->rd->online);
for_each_cpu_mask(i, tmp) {
if (idle_cpu(i)) {
if (i != task_cpu(p)) {
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 24621ce..d93169d 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -936,13 +936,6 @@ 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.
- */
- cpus_and(*lowest_mask, *lowest_mask, cpu_active_map);
- /*
* 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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