[PATCH 3/4] Eliminate lock_cpu_hotplug in kernel/sched.c

Gautham R Shenoy
2006-11-14T12:23:16Z

Eliminate lock_cpu_hotplug from kernel/sched.c and use sched_hotcpu_mutex
instead to postpone a hotplug event.

In the migration_call hotcpu callback function, take sched_hotcpu_mutex
while handling the event CPU_LOCK_ACQUIRE and release it while handling
CPU_LOCK_RELEASE event.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>

--
kernel/sched.c | 29 +++++++++++++++++++----------
1 files changed, 19 insertions(+), 10 deletions(-)

Index: hotplug/kernel/sched.c
===================================================================
--- hotplug.orig/kernel/sched.c
+++ hotplug/kernel/sched.c
@@ -267,6 +267,7 @@ struct rq {
};

static DEFINE_PER_CPU(struct rq, runqueues);
+static DEFINE_MUTEX(sched_hotcpu_mutex);

static inline int cpu_of(struct rq *rq)
{
@@ -4327,13 +4328,13 @@ long sched_setaffinity(pid_t pid, cpumas
struct task_struct *p;
int retval;

- lock_cpu_hotplug();
+ mutex_lock(&sched_hotcpu_mutex);
read_lock(&tasklist_lock);

p = find_process_by_pid(pid);
if (!p) {
read_unlock(&tasklist_lock);
- unlock_cpu_hotplug();
+ mutex_unlock(&sched_hotcpu_mutex);
return -ESRCH;
}

@@ -4360,7 +4361,7 @@ long sched_setaffinity(pid_t pid, cpumas

out_unlock:
put_task_struct(p);
- unlock_cpu_hotplug();
+ mutex_unlock(&sched_hotcpu_mutex);
return retval;
}

@@ -4417,7 +4418,7 @@ long sched_getaffinity(pid_t pid, cpumas
struct task_struct *p;
int retval;

- lock_cpu_hotplug();
+ mutex_lock(&sched_hotcpu_mutex);
read_lock(&tasklist_lock);

retval = -ESRCH;
@@ -4433,7 +4434,7 @@ long sched_getaffinity(pid_t pid, cpumas

out_unlock:
read_unlock(&tasklist_lock);
- unlock_cpu_hotplug();
+ mutex_unlock(&sched_hotcpu_mutex);
if (retval)
return retval;

@@ -5225,6 +5226,10 @@ migration_call(struct notifier_block *nf
struct rq *rq;

switch (action) {
+ case CPU_LOCK_ACQUIRE:
+ mutex_lock(&sched_hotcpu_mutex);
+ break;
+
case CPU_UP_PREPARE:
p = kthread_create(migration_thread, hcpu, "migration/%d",cpu);
if (IS_ERR(p))
@@ -5270,7 +5275,7 @@ migration_call(struct notifier_block *nf
BUG_ON(rq->nr_running != 0);

/* No need to migrate the tasks: it was best-effort if
- * they didn't do lock_cpu_hotplug(). Just wake up
+ * they didn't take sched_hotcpu_mutex. Just wake up
* the requestors. */
spin_lock_irq(&rq->lock);
while (!list_empty(&rq->migration_queue)) {
@@ -5283,6 +5288,10 @@ migration_call(struct notifier_block *nf
}
spin_unlock_irq(&rq->lock);
break;
+
+ case CPU_LOCK_RELEASE:
+ mutex_unlock(&sched_hotcpu_mutex);
+ break;
#endif
}
return NOTIFY_OK;
@@ -6652,10 +6661,10 @@ int arch_reinit_sched_domains(void)
{
int err;

- lock_cpu_hotplug();
+ mutex_lock(&sched_hotcpu_mutex);
detach_destroy_domains(&cpu_online_map);
err = arch_init_sched_domains(&cpu_online_map);
- unlock_cpu_hotplug();
+ mutex_unlock(&sched_hotcpu_mutex);

return err;
}
@@ -6763,12 +6772,12 @@ void __init sched_init_smp(void)
{
cpumask_t non_isolated_cpus;

- lock_cpu_hotplug();
+ mutex_lock(&sched_hotcpu_mutex);
arch_init_sched_domains(&cpu_online_map);
cpus_andnot(non_isolated_cpus, cpu_online_map, cpu_isolated_map);
if (cpus_empty(non_isolated_cpus))
cpu_set(smp_processor_id(), non_isolated_cpus);
- unlock_cpu_hotplug();
+ mutex_unlock(&sched_hotcpu_mutex);
/* XXX: Theoretical race here - CPU may be hotplugged now */
hotcpu_notifier(update_sched_domains, 0);