2.6.2-rc2-mm2 CPU Hotplug: cpu_active_map

Hi Andrew et al.

	Forward ported to -mm tree, so there might still be bugs.
Wanted to get these aired more widely.  Especially get Nick exposed to
the sched parts.

Name: Create cpu_active_map
Author: Rusty Russell
Status: Booted on 2.6.2-rc2-bk2

D: When CPUs are going down, there is a time when cpu_online(cpu) is
D: false, but they are still scheduling and responding to interrupts
D: (we are migrating things off the CPU, shutting down per-cpu
D: threads, etc).  It turns out that RCU cares about these CPUs, so
D: the decision was made to expose this mask (previously internal to x86,
D: and only used for IPIs).
D: 
D: The semantics of this mask are as follows:
D: 1) For platforms without hot unplug of CPUs: cpu_active_map ==
D:    cpu_online_map.
D: 2) For the others, they are equal except for a CPU which is going
D:    down: cpu_online_map gets cleared by __cpu_disable(), cpu_ipi_map
D:    gets cleared in __cpu_die() once the CPU is no longer responding
D:    to interrupts.

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .25707-linux-2.6.0-test11-bk7/include/linux/cpumask.h .25707-linux-2.6.0-test11-bk7.updated/include/linux/cpumask.h
--- .25707-linux-2.6.0-test11-bk7/include/linux/cpumask.h	2003-12-10 13:58:18.000000000 +1100
+++ .25707-linux-2.6.0-test11-bk7.updated/include/linux/cpumask.h	2003-12-10 14:01:29.000000000 +1100
@@ -43,6 +43,13 @@ typedef unsigned long cpumask_t;
 extern cpumask_t cpu_online_map;
 extern cpumask_t cpu_possible_map;
 
+#ifdef CONFIG_HOTPLUG_CPU
+/* Online, or on its way down but still receiving interrupts. */
+extern cpumask_t cpu_active_map;
+#else
+#define cpu_active_map cpu_online_map
+#endif
+
 #define num_online_cpus()		cpus_weight(cpu_online_map)
 #define cpu_online(cpu)			cpu_isset(cpu, cpu_online_map)
 #define cpu_possible(cpu)		cpu_isset(cpu, cpu_possible_map)
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .25707-linux-2.6.0-test11-bk7/kernel/rcupdate.c .25707-linux-2.6.0-test11-bk7.updated/kernel/rcupdate.c
--- .25707-linux-2.6.0-test11-bk7/kernel/rcupdate.c	2003-12-10 13:58:19.000000000 +1100
+++ .25707-linux-2.6.0-test11-bk7.updated/kernel/rcupdate.c	2003-12-10 14:01:03.000000000 +1100
@@ -110,7 +110,7 @@ static void rcu_start_batch(long newbatc
 	    !cpus_empty(rcu_ctrlblk.rcu_cpu_mask)) {
 		return;
 	}
-	rcu_ctrlblk.rcu_cpu_mask = cpu_online_map;
+	rcu_ctrlblk.rcu_cpu_mask = cpu_active_map;
 }
 
 /*
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
-
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