[PATCH] Use CPU_UP_PREPARE properly

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To: akpm@osdl.org
Date:	Sun, 25 Jan 2004 01:11:46 +1100

Hi Andrew,

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.

Name: Use CPU_UP_PREPARE notifier in sched.c and softirq.c
Author: Rusty Russell
Status: Experimental
Depends: Hotcpu/use-kthread-simple.patch.gz

D: The cpu hotplug code actually provides two notifiers: CPU_UP_PREPARE
D: which preceeds the online and can fail, and CPU_ONLINE which can't.
D:
D: Current usage is only done at boot, so this distinction doesn't
D: matter, but it's a bad example to set. This also means that the
D: migration threads do not have to be higher priority than the
D: others, since they are ready to go before any CPU_ONLINE callbacks
D: are done.

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .19555-linux-2.6.2-rc1-bk1/kernel/sched.c .19555-linux-2.6.2-rc1-bk1.updated/kernel/sched.c
--- .19555-linux-2.6.2-rc1-bk1/kernel/sched.c 2004-01-24 18:54:51.000000000 +1100
+++ .19555-linux-2.6.2-rc1-bk1.updated/kernel/sched.c 2004-01-24 18:54:52.000000000 +1100
@@ -2803,29 +2803,36 @@ 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. */
+/* 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,
+ .priority = -10,
 };
 
 __init int 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 -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .19555-linux-2.6.2-rc1-bk1/kernel/softirq.c .19555-linux-2.6.2-rc1-bk1.updated/kernel/softirq.c
--- .19555-linux-2.6.2-rc1-bk1/kernel/softirq.c 2004-01-24 18:54:51.000000000 +1100
+++ .19555-linux-2.6.2-rc1-bk1.updated/kernel/softirq.c 2004-01-24 18:54:52.000000000 +1100
@@ -367,8 +367,11 @@ 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);
@@ -376,7 +379,11 @@ 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;
 }
@@ -387,7 +394,9 @@ 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;
 }

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
-
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• Previous message: Serge Belyshev: "[PATCH] arch/i386/Makefile,scripts/gcc-version.sh,Makefile small fixes"
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