From: Rusty Russell <rusty@rustcorp.com.au>
The cpu hotplug code actually provides two notifiers: CPU_UP_PREPARE
which preceeds the online and can fail, and CPU_ONLINE which can't.
Current usage is only done at boot, so this distinction doesn't
matter, but it's a bad example to set. This also means that the
migration threads do not have to be higher priority than the
others, since they are ready to go before any CPU_ONLINE callbacks
are done.
This patch is experimental but fairly straight foward: I haven't been
able to test it since extracting it from the hotplug cpu code, so it's
possible I screwed something up.
---
kernel/sched.c | 23 +++++++++++++++--------
kernel/softirq.c | 15 ++++++++++++---
2 files changed, 27 insertions(+), 11 deletions(-)
diff -puN kernel/sched.c~use-CPU_UP_PREPARE-properly kernel/sched.c
--- 25/kernel/sched.c~use-CPU_UP_PREPARE-properly 2004-01-28 23:13:38.000000000 -0800
+++ 25-akpm/kernel/sched.c 2004-01-28 23:13:38.000000000 -0800
@@ -3125,29 +3125,36 @@ static int migration_call(struct notifie
struct task_struct *p;
switch (action) {
- case CPU_ONLINE:
+ case CPU_UP_PREPARE:
p = kthread_create(migration_thread, hcpu, "migration/%d",cpu);
if (IS_ERR(p))
return NOTIFY_BAD;
kthread_bind(p, cpu);
cpu_rq(cpu)->migration_thread = p;
- wake_up_process(p);
+ break;
+ case CPU_ONLINE:
+ /* Strictly unneccessary, as first user will wake it. */
+ wake_up_process(cpu_rq(cpu)->migration_thread);
break;
}
return NOTIFY_OK;
}
-/* Want this before the other threads, so they can use set_cpus_allowed. */
-static struct notifier_block migration_notifier = {
- .notifier_call = &migration_call,
- .priority = 10,
+/*
+ * We want this after the other threads, so they can use set_cpus_allowed
+ * from their CPU_OFFLINE callback
+ */
+static struct notifier_block __devinitdata migration_notifier = {
+ .notifier_call = migration_call,
+ .priority = -10,
};
int __init migration_init(void)
{
+ void *cpu = (void *)(long)smp_processor_id();
/* Start one for boot CPU. */
- migration_call(&migration_notifier, CPU_ONLINE,
- (void *)(long)smp_processor_id());
+ migration_call(&migration_notifier, CPU_UP_PREPARE, cpu);
+ migration_call(&migration_notifier, CPU_ONLINE, cpu);
register_cpu_notifier(&migration_notifier);
return 0;
}
diff -puN kernel/softirq.c~use-CPU_UP_PREPARE-properly kernel/softirq.c
--- 25/kernel/softirq.c~use-CPU_UP_PREPARE-properly 2004-01-28 23:13:38.000000000 -0800
+++ 25-akpm/kernel/softirq.c 2004-01-28 23:13:38.000000000 -0800
@@ -351,7 +351,10 @@ static int __devinit cpu_callback(struct
int hotcpu = (unsigned long)hcpu;
struct task_struct *p;
- if (action == CPU_ONLINE) {
+ switch (action) {
+ case CPU_UP_PREPARE:
+ BUG_ON(per_cpu(tasklet_vec, hotcpu).list);
+ BUG_ON(per_cpu(tasklet_hi_vec, hotcpu).list);
p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
if (IS_ERR(p)) {
printk("ksoftirqd for %i failed\n", hotcpu);
@@ -359,7 +362,11 @@ static int __devinit cpu_callback(struct
}
per_cpu(ksoftirqd, hotcpu) = p;
kthread_bind(p, hotcpu);
- wake_up_process(p);
+ per_cpu(ksoftirqd, hotcpu) = p;
+ break;
+ case CPU_ONLINE:
+ wake_up_process(per_cpu(ksoftirqd, hotcpu));
+ break;
}
return NOTIFY_OK;
}
@@ -370,7 +377,9 @@ static struct notifier_block __devinitda
__init int spawn_ksoftirqd(void)
{
- cpu_callback(&cpu_nfb, CPU_ONLINE, (void *)(long)smp_processor_id());
+ void *cpu = (void *)(long)smp_processor_id();
+ cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
+ cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
register_cpu_notifier(&cpu_nfb);
return 0;
}
_