[PATCH] 2.5.25 Hotplug CPU boot changes

[PATCH] 2.5.25 Hotplug CPU boot changes

[Rusty Russell]

The following patches change boot sequence, and once Linus releases
2.5.26, I'll be updating and sending them.  This will break every SMP
architecture (patch for x86 below, and I have a patch for PPC32).

Feedback welcome,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Name: Hot-plug CPU Boot Changes
Author: Rusty Russell
Status: Tested on 2.5.25, x86 SMP

D: This patch alters the boot sequence to "plug in" each CPU, one at a
D: time.  You need the patch for each architecture, as well.  The
D: interface used to be "smp_boot_cpus()", "smp_commence()", and each
D: arch implemented the "maxcpus" boot arg itself.  With this patch,
D: it is:
D:   smp_prepare_cpus(maxcpus): probe for cpus and set up cpu_possible(cpu).
D:   __cpu_up(cpu): called *after* initcalls, for each cpu where
D:      cpu_possible(cpu) is true.
D:   smp_cpus_done(maxcpus): called after every cpu has been brought up

diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/include/linux/notifier.h working-2.5.25-hotcpu/include/linux/notifier.h
--- linux-2.5.25/include/linux/notifier.h	Mon Jun 24 00:55:28 2002
+++ working-2.5.25-hotcpu/include/linux/notifier.h	Mon Jul 15 12:44:55 2002
@@ -58,5 +58,7 @@
 #define SYS_HALT	0x0002	/* Notify of system halt */
 #define SYS_POWER_OFF	0x0003	/* Notify of system power off */
 
+#define CPU_ONLINE	0x0002 /* CPU (unsigned)v coming up */
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/include/linux/sched.h working-2.5.25-hotcpu/include/linux/sched.h
--- linux-2.5.25/include/linux/sched.h	Sun Jul  7 02:12:24 2002
+++ working-2.5.25-hotcpu/include/linux/sched.h	Mon Jul 15 12:44:55 2002
@@ -150,7 +150,6 @@
 extern void update_one_process(struct task_struct *p, unsigned long user,
 			       unsigned long system, int cpu);
 extern void scheduler_tick(int user_tick, int system);
-extern void migration_init(void);
 extern unsigned long cache_decay_ticks;
 
 
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/include/linux/smp.h working-2.5.25-hotcpu/include/linux/smp.h
--- linux-2.5.25/include/linux/smp.h	Fri Jun 21 09:41:55 2002
+++ working-2.5.25-hotcpu/include/linux/smp.h	Mon Jul 15 14:45:56 2002
@@ -32,19 +32,19 @@
 
 
 /*
- * Boot processor call to load the other CPU's
+ * Prepare machine for booting other CPUs.
  */
-extern void smp_boot_cpus(void);
+extern void smp_prepare_cpus(unsigned int max_cpus);
 
 /*
- * Processor call in. Must hold processors until ..
+ * Bring a CPU up
  */
-extern void smp_callin(void);
+extern int __cpu_up(unsigned int cpunum);
 
 /*
- * Multiprocessors may now schedule
+ * Final polishing of CPUs
  */
-extern void smp_commence(void);
+extern void smp_cpus_done(unsigned int max_cpus);
 
 /*
  * Call a function on all other processors
@@ -71,6 +71,13 @@
 #define MSG_RESCHEDULE		0x0003	/* Reschedule request from master CPU*/
 #define MSG_CALL_FUNCTION       0x0004  /* Call function on all other CPUs */
 
+struct notifier_block;
+
+/* Need to know about CPUs going up/down? */
+extern int register_cpu_notifier(struct notifier_block *nb);
+extern void unregister_cpu_notifier(struct notifier_block *nb);
+
+int cpu_up(unsigned int cpu);
 #else /* !SMP */
 
 /*
@@ -92,6 +99,10 @@
 #define __per_cpu_data
 #define per_cpu(var, cpu)			var
 #define this_cpu(var)				var
+
+/* Need to know about CPUs going up/down? */
+#define register_cpu_notifier(nb) 0
+#define unregister_cpu_notifier(nb) do { } while(0)
 
 #endif /* !SMP */
 
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/init/main.c working-2.5.25-hotcpu/init/main.c
--- linux-2.5.25/init/main.c	Thu Jun 20 01:28:52 2002
+++ working-2.5.25-hotcpu/init/main.c	Mon Jul 15 12:44:55 2002
@@ -93,6 +93,35 @@
 
 char *execute_command;
 
+/* Setup configured maximum number of CPUs to activate */
+static unsigned int max_cpus = UINT_MAX;
+
+/*
+ * Setup routine for controlling SMP activation
+ *
+ * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
+ * activation entirely (the MPS table probe still happens, though).
+ *
+ * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
+ * greater than 0, limits the maximum number of CPUs activated in
+ * SMP mode to <NUM>.
+ */
+static int __init nosmp(char *str)
+{
+	max_cpus = 0;
+	return 1;
+}
+
+__setup("nosmp", nosmp);
+
+static int __init maxcpus(char *str)
+{
+	get_option(&str, &max_cpus);
+	return 1;
+}
+
+__setup("maxcpus=", maxcpus);
+
 static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
 char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
 
@@ -273,6 +302,7 @@
 #endif
 
 static inline void setup_per_cpu_areas(void) { }
+static inline void smp_prepare_cpus(unsigned int maxcpus) { }
 
 #else
 
@@ -303,11 +333,27 @@
 /* Called by boot processor to activate the rest. */
 static void __init smp_init(void)
 {
+	unsigned int i;
+
+	/* FIXME: This should be done in userspace --RR */
+	for (i = 0; i < NR_CPUS; i++) {
+		if (num_online_cpus() >= max_cpus)
+			break;
+		if (cpu_possible(i) && !cpu_online(i)) {
+			printk("Bringing up %in", i);
+			cpu_up(i);
+		}
+	}
+
+	/* Any cleanup work */
+	printk("CPUS done %un", max_cpus);
+	smp_cpus_done(max_cpus);
+#if 0
 	/* Get other processors into their bootup holding patterns. */
-	smp_boot_cpus();
 
 	smp_threads_ready=1;
 	smp_commence();
+#endif
 }
 
 #endif
@@ -402,14 +448,12 @@
 	check_bugs();
 	printk("POSIX conformance testing by UNIFIXn");
 
-	init_idle(current, smp_processor_id());
-
 	/* 
 	 *	We count on the initial thread going ok 
 	 *	Like idlers init is an unlocked kernel thread, which will
 	 *	make syscalls (and thus be locked).
 	 */
-	smp_init();
+	init_idle(current, smp_processor_id());
 
 	/* Do the rest non-__init'ed, we're now alive */
 	rest_init();
@@ -441,12 +485,6 @@
 static void __init do_basic_setup(void)
 {
 	/*
-	 * Let the per-CPU migration threads start up:
-	 */
-#if CONFIG_SMP
-	migration_init();
-#endif
-	/*
 	 * Tell the world that we're going to be the grim
 	 * reaper of innocent orphaned children.
 	 *
@@ -490,7 +528,10 @@
 	static char * argv_sh[] = { "sh", NULL, };
 
 	lock_kernel();
+	/* Sets up cpus_possible() */
+	smp_prepare_cpus(max_cpus);
 	do_basic_setup();
+	smp_init();
 
 	prepare_namespace();
 
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/kernel/Makefile working-2.5.25-hotcpu/kernel/Makefile
--- linux-2.5.25/kernel/Makefile	Mon Jun 10 16:03:56 2002
+++ working-2.5.25-hotcpu/kernel/Makefile	Mon Jul 15 12:44:55 2002
@@ -17,6 +17,7 @@
 	    sysctl.o capability.o ptrace.o timer.o user.o 
 	    signal.o sys.o kmod.o context.o futex.o platform.o
 
+obj-$(CONFIG_SMP) += cpu.o
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULES) += ksyms.o
 obj-$(CONFIG_PM) += pm.o
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/kernel/cpu.c working-2.5.25-hotcpu/kernel/cpu.c
--- linux-2.5.25/kernel/cpu.c	Thu Jan  1 10:00:00 1970
+++ working-2.5.25-hotcpu/kernel/cpu.c	Mon Jul 15 14:34:49 2002
@@ -0,0 +1,54 @@
+/* CPU control.
+ * (C) 2001 Rusty Russell
+ * This code is licenced under the GPL.
+ */
+#include <linux/proc_fs.h>
+#include <linux/smp.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <linux/sched.h>
+#include <linux/unistd.h>
+#include <asm/semaphore.h>
+
+/* This protects CPUs going up and down... */
+DECLARE_MUTEX(cpucontrol);
+
+static struct notifier_block *cpu_chain = NULL;
+
+/* Need to know about CPUs going up/down? */
+int register_cpu_notifier(struct notifier_block *nb)
+{
+	return notifier_chain_register(&cpu_chain, nb);
+}
+
+void unregister_cpu_notifier(struct notifier_block *nb)
+{
+	notifier_chain_unregister(&cpu_chain,nb);
+}
+
+int __devinit cpu_up(unsigned int cpu)
+{
+	int ret;
+
+	if ((ret = down_interruptible(&cpucontrol)) != 0) 
+		return ret;
+
+	if (cpu_online(cpu)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* Arch-specific enabling code. */
+	ret = __cpu_up(cpu);
+	if (ret != 0) goto out;
+	if (!cpu_online(cpu))
+		BUG();
+
+	/* Now call notifier in preparation. */
+	printk("CPU %u IS NOW UP!n", cpu);
+	notifier_call_chain(&cpu_chain, CPU_ONLINE, (void *)cpu);
+
+ out:
+	up(&cpucontrol);
+	return ret;
+}
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/kernel/sched.c working-2.5.25-hotcpu/kernel/sched.c
--- linux-2.5.25/kernel/sched.c	Sun Jul  7 02:12:24 2002
+++ working-2.5.25-hotcpu/kernel/sched.c	Mon Jul 15 12:44:55 2002
@@ -26,6 +26,8 @@
 #include <linux/interrupt.h>
 #include <linux/completion.h>
 #include <linux/kernel_stat.h>
+#include <linux/notifier.h>
+#include <linux/delay.h>
 
 /*
  * Convert user-nice values [ -20 ... 0 ... 19 ]
@@ -1752,9 +1756,11 @@
 	migration_req_t req;
 	runqueue_t *rq;
 
+#if 0 /* FIXME: Grab cpu_lock, return error on this case. --RR */
 	new_mask &= cpu_online_map;
 	if (!new_mask)
 		BUG();
+#endif
 
 	preempt_disable();
 	rq = task_rq_lock(p, &flags);
@@ -1787,8 +1793,6 @@
 	preempt_enable();
 }
 
-static __initdata int master_migration_thread;
-
 static int migration_thread(void * bind_cpu)
 {
 	int cpu = (int) (long) bind_cpu;
@@ -1800,15 +1804,7 @@
 	sigfillset(&current->blocked);
 	set_fs(KERNEL_DS);
 
-	/*
-	 * The first migration thread is started on the boot CPU, it
-	 * migrates the other migration threads to their destination CPUs.
-	 */
-	if (cpu != master_migration_thread) {
-		while (!cpu_rq(master_migration_thread)->migration_thread)
-			yield();
-		set_cpus_allowed(current, 1UL << cpu);
-	}
+	set_cpus_allowed(current, 1UL << cpu);
 	printk("migration_task %d on cpu=%dn", cpu, smp_processor_id());
 	ret = setscheduler(0, SCHED_FIFO, &param);
 
@@ -1865,27 +1861,31 @@
 	}
 }
 
-void __init migration_init(void)
+static int migration_call(struct notifier_block *nfb,
+			  unsigned long action,
+			  void *hcpu)
 {
-	int cpu;
-
-	master_migration_thread = smp_processor_id();
-	current->cpus_allowed = 1UL << master_migration_thread;
-	
-	for (cpu = 0; cpu < NR_CPUS; cpu++) {
-		if (!cpu_online(cpu))
-			continue;
-		if (kernel_thread(migration_thread, (void *) (long) cpu,
-				CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0)
-			BUG();
+	switch (action) {
+	case CPU_ONLINE:
+		printk("Starting migration thread for cpu %lin",
+		       (long)hcpu);
+		kernel_thread(migration_thread, hcpu,
+			      CLONE_FS | CLONE_FILES | CLONE_SIGNAL);
+		break;
 	}
-	current->cpus_allowed = -1L;
+	return NOTIFY_OK;
+}
 
-	for (cpu = 0; cpu < NR_CPUS; cpu++) {
-		if (!cpu_online(cpu))
-			continue;
-		while (!cpu_rq(cpu)->migration_thread)
-			schedule_timeout(2);
-	}
+static struct notifier_block migration_notifier = { &migration_call, NULL, 0 };
+
+int __init migration_init(void)
+{
+	/* Start one for boot CPU. */
+	migration_call(&migration_notifier, CPU_ONLINE,
+		       (void *)smp_processor_id());
+	register_cpu_notifier(&migration_notifier);
+	return 0;
 }
+
+__initcall(migration_init);
 #endif
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/kernel/softirq.c working-2.5.25-hotcpu/kernel/softirq.c
--- linux-2.5.25/kernel/softirq.c	Sun Jul  7 02:12:24 2002
+++ working-2.5.25-hotcpu/kernel/softirq.c	Mon Jul 15 12:44:55 2002
@@ -17,6 +17,7 @@
 #include <linux/init.h>
 #include <linux/tqueue.h>
 #include <linux/percpu.h>
+#include <linux/notifier.h>
 
 /*
    - No shared variables, all the data are CPU local.
@@ -397,20 +398,32 @@
 	}
 }
 
-static __init int spawn_ksoftirqd(void)
+static int __devinit cpu_callback(struct notifier_block *nfb,
+				  unsigned long action,
+				  void *hcpu)
 {
-	int cpu;
+	int hotcpu = (unsigned long)hcpu;
 
-	for (cpu = 0; cpu < NR_CPUS; cpu++) {
-		if (!cpu_online(cpu))
-			continue;
-		if (kernel_thread(ksoftirqd, (void *) (long) cpu,
-				  CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0)
-			printk("spawn_ksoftirqd() failed for cpu %dn", cpu);
-		else
-			while (!ksoftirqd_task(cpu))
-				yield();
-	}
+	if (action == CPU_ONLINE) {
+		if (kernel_thread(ksoftirqd, hcpu,
+				  CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0) {
+			printk("ksoftirqd for %i failedn", hotcpu);
+			return NOTIFY_BAD;
+		}
+
+		while (!ksoftirqd_task(hotcpu))
+			yield();
+		return NOTIFY_OK;
+ 	}
+	return NOTIFY_BAD;
+}
+
+static struct notifier_block cpu_nfb = { &cpu_callback, NULL, 0 };
+
+static __init int spawn_ksoftirqd(void)
+{
+	cpu_callback(&cpu_nfb, CPU_ONLINE, (void *)smp_processor_id());
+	register_cpu_notifier(&cpu_nfb);
 	return 0;
 }
 
Name: Hot-plug CPU Boot Rewrite for i386
Author: Rusty Russell
Status: Tested 2.5.25, dual SMP
Depends: Hotcpu/hotcpu-boot.patch.gz

D: This modifies the i386 boot sequence to "plug in" CPUs one at a
D: time.  This is the minimal change to make it work (the CPUs are
D: brought up as normal during the "smp_prepare_cpus()" probe phase).

diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/arch/i386/kernel/apic.c working-2.5.25-hotcpu/arch/i386/kernel/apic.c
--- linux-2.5.25/arch/i386/kernel/apic.c	Thu Jun 20 01:28:47 2002
+++ working-2.5.25-hotcpu/arch/i386/kernel/apic.c	Mon Jul 15 18:23:12 2002
@@ -798,9 +798,9 @@
 	apic_write_around(APIC_TMICT, clocks/APIC_DIVISOR);
 }
 
-void setup_APIC_timer(void * data)
+static void setup_APIC_timer(unsigned int clocks)
 {
-	unsigned int clocks = (unsigned int) data, slice, t0, t1;
+	unsigned int slice, t0, t1;
 	unsigned long flags;
 	int delta;
 
@@ -926,7 +926,7 @@
 
 int dont_use_local_apic_timer __initdata = 0;
 
-void __init setup_APIC_clocks (void)
+void __init setup_boot_APIC_clock(void)
 {
 	/* Disabled by DMI scan or kernel option? */
 	if (dont_use_local_apic_timer)
@@ -941,12 +941,16 @@
 	/*
 	 * Now set up the timer for real.
 	 */
-	setup_APIC_timer((void *)calibration_result);
+	setup_APIC_timer(calibration_result);
 
 	__sti();
+}
 
-	/* and update all other cpus */
-	smp_call_function(setup_APIC_timer, (void *)calibration_result, 1, 1);
+void __init setup_secondary_APIC_clock(void)
+{
+	__cli(); /* FIXME: Do we need this? --RR */
+	setup_APIC_timer(calibration_result);
+	__sti();
 }
 
 void __init disable_APIC_timer(void)
@@ -1178,7 +1182,7 @@
 		if (!skip_ioapic_setup && nr_ioapics)
 			setup_IO_APIC();
 #endif
-	setup_APIC_clocks();
+	setup_boot_APIC_clock();
 
 	return 0;
 }
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/arch/i386/kernel/apm.c working-2.5.25-hotcpu/arch/i386/kernel/apm.c
--- linux-2.5.25/arch/i386/kernel/apm.c	Sun Jul  7 02:12:17 2002
+++ working-2.5.25-hotcpu/arch/i386/kernel/apm.c	Mon Jul 15 14:42:18 2002
@@ -1587,7 +1587,7 @@
 
 	p = buf;
 
-	if ((num_online_cpus() == 1) &&
+	if ((num_possible_cpus() == 1) &&
 	    !(error = apm_get_power_status(&bx, &cx, &dx))) {
 		ac_line_status = (bx >> 8) & 0xff;
 		battery_status = bx & 0xff;
@@ -1718,7 +1718,7 @@
 		}
 	}
 
-	if (debug && (num_online_cpus() == 1)) {
+	if (debug && (num_possible_cpus() == 1)) {
 		error = apm_get_power_status(&bx, &cx, &dx);
 		if (error)
 			printk(KERN_INFO "apm: power status not availablen");
@@ -1762,7 +1762,7 @@
 		pm_power_off = apm_power_off;
 	register_sysrq_key('o', &sysrq_poweroff_op);
 
-	if (num_online_cpus() == 1) {
+	if (num_possible_cpus() == 1) {
 #if defined(CONFIG_APM_DISPLAY_BLANK) && defined(CONFIG_VT)
 		console_blank_hook = apm_console_blank;
 #endif
@@ -1905,9 +1905,7 @@
 		printk(KERN_NOTICE "apm: disabled on user request.n");
 		return -ENODEV;
 	}
-	/* FIXME: When boot code changes, this will need to be
-           deactivated when/if a CPU comes up --RR */
-	if ((num_online_cpus() > 1) && !power_off) {
+	if ((num_possible_cpus() > 1) && !power_off) {
 		printk(KERN_NOTICE "apm: disabled - APM is not SMP safe.n");
 		return -ENODEV;
 	}
@@ -1961,9 +1959,7 @@
 
 	kernel_thread(apm, NULL, CLONE_FS | CLONE_FILES | CLONE_SIGHAND | SIGCHLD);
 
-	/* FIXME: When boot code changes, this will need to be
-           deactivated when/if a CPU comes up --RR */
-	if (num_online_cpus() > 1) {
+	if (num_possible_cpus() > 1) {
 		printk(KERN_NOTICE
 		   "apm: disabled - APM is not SMP safe (power off active).n");
 		return 0;
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/arch/i386/kernel/mtrr.c working-2.5.25-hotcpu/arch/i386/kernel/mtrr.c
--- linux-2.5.25/arch/i386/kernel/mtrr.c	Thu Jun 20 01:28:47 2002
+++ working-2.5.25-hotcpu/arch/i386/kernel/mtrr.c	Mon Jul 15 14:42:42 2002
@@ -1055,7 +1055,7 @@
     wait_barrier_cache_disable = TRUE;
     wait_barrier_execute = TRUE;
     wait_barrier_cache_enable = TRUE;
-    atomic_set (&undone_count, num_online_cpus() - 1);
+    atomic_set (&undone_count, num_booting_cpus() - 1);
     /*  Start the ball rolling on other CPUs  */
     if (smp_call_function (ipi_handler, &data, 1, 0) != 0)
 	panic ("mtrr: timed out waiting for other CPUsn");
@@ -1064,14 +1064,14 @@
     /*  Wait for all other CPUs to flush and disable their caches  */
     while (atomic_read (&undone_count) > 0) { rep_nop(); barrier(); }
     /* Set up for completion wait and then release other CPUs to change MTRRs*/
-    atomic_set (&undone_count, num_online_cpus() - 1);
+    atomic_set (&undone_count, num_booting_cpus() - 1);
     wait_barrier_cache_disable = FALSE;
     set_mtrr_cache_disable (&ctxt);
 
     /*  Wait for all other CPUs to flush and disable their caches  */
     while (atomic_read (&undone_count) > 0) { rep_nop(); barrier(); }
     /* Set up for completion wait and then release other CPUs to change MTRRs*/
-    atomic_set (&undone_count, num_online_cpus() - 1);
+    atomic_set (&undone_count, num_booting_cpus() - 1);
     wait_barrier_execute = FALSE;
     (*set_mtrr_up) (reg, base, size, type, FALSE);
     /*  Now wait for other CPUs to complete the function  */
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/arch/i386/kernel/nmi.c working-2.5.25-hotcpu/arch/i386/kernel/nmi.c
--- linux-2.5.25/arch/i386/kernel/nmi.c	Thu Jun 20 01:28:47 2002
+++ working-2.5.25-hotcpu/arch/i386/kernel/nmi.c	Mon Jul 15 15:30:34 2002
@@ -81,6 +81,8 @@
 	sti();
 	mdelay((10*1000)/nmi_hz); // wait 10 ticks
 
+	/* FIXME: Only boot CPU is online at this stage.  Check CPUs
+           as they come up. */
 	for (cpu = 0; cpu < NR_CPUS; cpu++) {
 		if (!cpu_online(cpu))
 			continue;
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/arch/i386/kernel/smpboot.c working-2.5.25-hotcpu/arch/i386/kernel/smpboot.c
--- linux-2.5.25/arch/i386/kernel/smpboot.c	Fri Jun 21 09:41:52 2002
+++ working-2.5.25-hotcpu/arch/i386/kernel/smpboot.c	Mon Jul 15 17:44:05 2002
@@ -31,7 +31,7 @@
  *	Maciej W. Rozycki	:	Bits for genuine 82489DX APICs
  *		Martin J. Bligh	: 	Added support for multi-quad systems
  *		Dave Jones	:	Report invalid combinations of Athlon CPUs.
- */
+*		Rusty Russell	:	Hacked into shape for new "hotplug" boot process. */
 
 #include <linux/config.h>
 #include <linux/init.h>
@@ -53,9 +53,6 @@
 /* Set if we find a B stepping CPU */
 static int __initdata smp_b_stepping;
 
-/* Setup configured maximum number of CPUs to activate */
-static int __initdata max_cpus = NR_CPUS;
-
 /* Number of siblings per CPU package */
 int smp_num_siblings = 1;
 int __initdata phys_proc_id[NR_CPUS]; /* Package ID of each logical CPU */
@@ -64,7 +61,8 @@
 unsigned long cpu_online_map;
 
 static volatile unsigned long cpu_callin_map;
-static volatile unsigned long cpu_callout_map;
+volatile unsigned long cpu_callout_map;
+static unsigned long smp_commenced_mask;
 
 /* Per CPU bogomips and other parameters */
 struct cpuinfo_x86 cpu_data[NR_CPUS] __cacheline_aligned;
@@ -73,33 +71,6 @@
 int smp_threads_ready;
 
 /*
- * Setup routine for controlling SMP activation
- *
- * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
- * activation entirely (the MPS table probe still happens, though).
- *
- * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
- * greater than 0, limits the maximum number of CPUs activated in
- * SMP mode to <NUM>.
- */
-
-static int __init nosmp(char *str)
-{
-	max_cpus = 0;
-	return 1;
-}
-
-__setup("nosmp", nosmp);
-
-static int __init maxcpus(char *str)
-{
-	get_option(&str, &max_cpus);
-	return 1;
-}
-
-__setup("maxcpus=", maxcpus);
-
-/*
  * Trampoline 80x86 program as an array.
  */
 
@@ -139,7 +110,7 @@
  * a given CPU
  */
 
-void __init smp_store_cpu_info(int id)
+static void __init smp_store_cpu_info(int id)
 {
 	struct cpuinfo_x86 *c = cpu_data + id;
 
@@ -193,29 +164,6 @@
 }
 
 /*
- * Architecture specific routine called by the kernel just before init is
- * fired off. This allows the BP to have everything in order [we hope].
- * At the end of this all the APs will hit the system scheduling and off
- * we go. Each AP will load the system gdt's and jump through the kernel
- * init into idle(). At this point the scheduler will one day take over
- * and give them jobs to do. smp_callin is a standard routine
- * we use to track CPUs as they power up.
- */
-
-static atomic_t smp_commenced = ATOMIC_INIT(0);
-
-void __init smp_commence(void)
-{
-	/*
-	 * Lets the callins below out of their loop.
-	 */
-	Dprintk("Setting commenced=1, go go gon");
-
-	wmb();
-	atomic_set(&smp_commenced,1);
-}
-
-/*
  * TSC synchronization.
  *
  * We first check wether all CPUs have their TSC's synchronized,
@@ -268,7 +216,7 @@
 	unsigned long one_usec;
 	int buggy = 0;
 
-	printk("checking TSC synchronization across CPUs: ");
+	printk("checking TSC synchronization across %u CPUs: ", num_booting_cpus());
 
 	one_usec = ((1<<30)/fast_gettimeoffset_quotient)*(1<<2);
 
@@ -289,7 +237,7 @@
 		/*
 		 * all APs synchronize but they loop on '== num_cpus'
 		 */
-		while (atomic_read(&tsc_count_start) != num_online_cpus()-1)
+		while (atomic_read(&tsc_count_start) != num_booting_cpus()-1)
 			mb();
 		atomic_set(&tsc_count_stop, 0);
 		wmb();
@@ -308,7 +256,7 @@
 		/*
 		 * Wait for all APs to leave the synchronization point:
 		 */
-		while (atomic_read(&tsc_count_stop) != num_online_cpus()-1)
+		while (atomic_read(&tsc_count_stop) != num_booting_cpus()-1)
 			mb();
 		atomic_set(&tsc_count_start, 0);
 		wmb();
@@ -317,16 +265,16 @@
 
 	sum = 0;
 	for (i = 0; i < NR_CPUS; i++) {
-		if (cpu_online(i)) {
+		if (test_bit(i, &cpu_callout_map)) {
 			t0 = tsc_values[i];
 			sum += t0;
 		}
 	}
-	avg = div64(sum, num_online_cpus());
+	avg = div64(sum, num_booting_cpus());
 
 	sum = 0;
 	for (i = 0; i < NR_CPUS; i++) {
-		if (!cpu_online(i))
+		if (!test_bit(i, &cpu_callout_map))
 			continue;
 		delta = tsc_values[i] - avg;
 		if (delta < 0)
@@ -359,7 +307,7 @@
 	int i;
 
 	/*
-	 * num_online_cpus is not necessarily known at the time
+	 * Not every cpu is online at the time
 	 * this gets called, so we first wait for the BP to
 	 * finish SMP initialization:
 	 */
@@ -367,7 +315,7 @@
 
 	for (i = 0; i < NR_LOOPS; i++) {
 		atomic_inc(&tsc_count_start);
-		while (atomic_read(&tsc_count_start) != num_online_cpus())
+		while (atomic_read(&tsc_count_start) != num_booting_cpus())
 			mb();
 
 		rdtscll(tsc_values[smp_processor_id()]);
@@ -375,7 +323,7 @@
 			write_tsc(0, 0);
 
 		atomic_inc(&tsc_count_stop);
-		while (atomic_read(&tsc_count_stop) != num_online_cpus()) mb();
+		while (atomic_read(&tsc_count_stop) != num_booting_cpus()) mb();
 	}
 }
 #undef NR_LOOPS
@@ -403,7 +351,7 @@
 	 */
 	phys_id = GET_APIC_ID(apic_read(APIC_ID));
 	cpuid = smp_processor_id();
-	if (test_and_set_bit(cpuid, &cpu_online_map)) {
+	if (test_bit(cpuid, &cpu_callin_map)) {
 		printk("huh, phys CPU#%d, CPU#%d already present??n",
 					phys_id, cpuid);
 		BUG();
@@ -501,15 +449,17 @@
 	 */
 	cpu_init();
 	smp_callin();
-	while (!atomic_read(&smp_commenced))
+	while (!test_bit(smp_processor_id(), &smp_commenced_mask))
 		rep_nop();
+	setup_secondary_APIC_clock();
 	enable_APIC_timer();
 	/*
 	 * low-memory mappings have been cleared, flush them from
 	 * the local TLBs too.
 	 */
 	local_flush_tlb();
-
+	set_bit(smp_processor_id(), &cpu_online_map);
+	wmb();
 	return cpu_idle();
 }
 
@@ -943,7 +893,6 @@
 		unmap_cpu_to_boot_apicid(cpu, apicid);
 		clear_bit(cpu, &cpu_callout_map); /* was set here (do_boot_cpu()) */
 		clear_bit(cpu, &cpu_initialized); /* was set by cpu_init() */
-		clear_bit(cpu, &cpu_online_map);  /* was set in smp_callin() */
 		cpucount--;
 	}
 
@@ -1015,7 +964,7 @@
 
 int cpu_sibling_map[NR_CPUS] __cacheline_aligned;
 
-void __init smp_boot_cpus(void)
+static void __init smp_boot_cpus(unsigned int max_cpus)
 {
 	int apicid, cpu, bit;
 
@@ -1057,6 +1006,7 @@
 	 * We have the boot CPU online for sure.
 	 */
 	set_bit(0, &cpu_online_map);
+	set_bit(0, &cpu_callout_map);
 	boot_cpu_logical_apicid = logical_smp_processor_id();
 	map_cpu_to_boot_apicid(0, boot_cpu_apicid);
 
@@ -1073,11 +1023,11 @@
 #ifndef CONFIG_VISWS
 		io_apic_irqs = 0;
 #endif
-		cpu_online_map = phys_cpu_present_map = 1;
+		phys_cpu_present_map = 1;
 		if (APIC_init_uniprocessor())
 			printk(KERN_NOTICE "Local APIC not detected."
 					   " Using dummy APIC emulation.n");
-		goto smp_done;
+		return;
 	}
 
 	/*
@@ -1102,8 +1052,8 @@
 #ifndef CONFIG_VISWS
 		io_apic_irqs = 0;
 #endif
-		cpu_online_map = phys_cpu_present_map = 1;
-		goto smp_done;
+		phys_cpu_present_map = 1;
+		return;
 	}
 
 	verify_local_APIC();
@@ -1117,8 +1067,8 @@
 #ifndef CONFIG_VISWS
 		io_apic_irqs = 0;
 #endif
-		cpu_online_map = phys_cpu_present_map = 1;
-		goto smp_done;
+		phys_cpu_present_map = 1;
+		return;
 	}
 
 	connect_bsp_APIC();
@@ -1190,7 +1140,7 @@
 	} else {
 		unsigned long bogosum = 0;
 		for (cpu = 0; cpu < NR_CPUS; cpu++)
-			if (cpu_online_map & (1<<cpu))
+			if (cpu_callout_map & (1<<cpu))
 				bogosum += cpu_data[cpu].loops_per_jiffy;
 		printk(KERN_INFO "Total of %d processors activated (%lu.%02lu BogoMIPS).n",
 			cpucount+1,
@@ -1213,10 +1163,10 @@
 		
 		for (cpu = 0; cpu < NR_CPUS; cpu++) {
 			int 	i;
-			if (!cpu_online(cpu)) continue;
+			if (!test_bit(cpu, &cpu_callout_map)) continue;
 
 			for (i = 0; i < NR_CPUS; i++) {
-				if (i == cpu || !cpu_online(i))
+				if (i == cpu || !test_bit(i, &cpu_callout_map))
 					continue;
 				if (phys_proc_id[cpu] == phys_proc_id[i]) {
 					cpu_sibling_map[cpu] = i;
@@ -1240,17 +1190,40 @@
 		setup_IO_APIC();
 #endif
 
-	/*
-	 * Set up all local APIC timers in the system:
-	 */
-	setup_APIC_clocks();
+	setup_boot_APIC_clock();
 
 	/*
 	 * Synchronize the TSC with the AP
 	 */
 	if (cpu_has_tsc && cpucount)
 		synchronize_tsc_bp();
+}
 
-smp_done:
+/* These are wrappers to interface to the new boot process.  Someone
+   who understands all this stuff should rewrite it properly. --RR 15/Jul/02 */
+void __init smp_prepare_cpus(unsigned int max_cpus)
+{
+	smp_boot_cpus(max_cpus);
+}
+
+int __devinit __cpu_up(unsigned int cpu)
+{
+	/* This only works at boot for x86.  See "rewrite" above. */
+	if (test_bit(cpu, &smp_commenced_mask))
+		return -ENOSYS;
+
+	/* In case one didn't come up */
+	if (!test_bit(cpu, &cpu_callin_map))
+		return -EIO;
+
+	/* Unleash the CPU! */
+	set_bit(cpu, &smp_commenced_mask);
+	while (!test_bit(cpu, &cpu_online_map))
+		mb();
+	return 0;
+}
+
+void __init smp_cpus_done(unsigned int max_cpus)
+{
 	zap_low_mappings();
 }
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/include/asm-i386/apic.h working-2.5.25-hotcpu/include/asm-i386/apic.h
--- linux-2.5.25/include/asm-i386/apic.h	Mon Apr 15 11:47:44 2002
+++ working-2.5.25-hotcpu/include/asm-i386/apic.h	Mon Jul 15 18:22:21 2002
@@ -76,7 +76,8 @@
 extern void setup_local_APIC (void);
 extern void init_apic_mappings (void);
 extern void smp_local_timer_interrupt (struct pt_regs * regs);
-extern void setup_APIC_clocks (void);
+extern void setup_boot_APIC_clock (void);
+extern void setup_secondary_APIC_clock (void);
 extern void setup_apic_nmi_watchdog (void);
 extern inline void nmi_watchdog_tick (struct pt_regs * regs);
 extern int APIC_init_uniprocessor (void);
diff -urN -I $.*$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.25/include/asm-i386/smp.h working-2.5.25-hotcpu/include/asm-i386/smp.h
--- linux-2.5.25/include/asm-i386/smp.h	Thu Jun 20 01:28:51 2002
+++ working-2.5.25-hotcpu/include/asm-i386/smp.h	Mon Jul 15 14:46:12 2002
@@ -79,19 +79,13 @@
 extern volatile int logical_apicid_to_cpu[MAX_APICID];
 
 /*
- * General functions that each host system must provide.
- */
- 
-extern void smp_boot_cpus(void);
-extern void smp_store_cpu_info(int id);		/* Store per CPU info (like the initial udelay numbers */
-
-/*
  * This function is needed by all SMP systems. It must _always_ be valid
  * from the initial startup. We map APIC_BASE very early in page_setup(),
  * so this is correct in the x86 case.
  */
 #define smp_processor_id() (current_thread_info()->cpu)
 
+#define cpu_possible(cpu) (phys_cpu_present_map & (1<<(cpu)))
 #define cpu_online(cpu) (cpu_online_map & (1<<(cpu)))
 
 extern inline unsigned int num_online_cpus(void)
@@ -117,6 +111,13 @@
 {
 	/* we don't want to mark this access volatile - bad code generation */
 	return GET_APIC_LOGICAL_ID(*(unsigned long *)(APIC_BASE+APIC_LDR));
+}
+
+extern volatile unsigned long cpu_callout_map;
+/* We don't mark CPUs online until __cpu_up(), so we need another measure */
+static inline int num_booting_cpus(void)
+{
+	return hweight32(cpu_callout_map);
 }
 
 #endif /* !__ASSEMBLY__ */

Re: [PATCH] 2.5.25 Hotplug CPU boot changes

[Alan Cox]

On Mon, 2002-07-15 at 09:58, Rusty Russell wrote:
> The following patches change boot sequence, and once Linus releases
> 2.5.26, I'll be updating and sending them.  This will break every SMP
> architecture (patch for x86 below, and I have a patch for PPC32).
>			printk("ksoftirqd for %i failedn", hotcpu);

Q: What prevents a CPU coming up -during- an MTRR change once the rest
of the cpu hot plugging is present ?

Re: [PATCH] 2.5.25 Hotplug CPU boot changes

[Dave Jones]

On Mon, Jul 15, 2002 at 01:29:01PM +0100, Alan Cox wrote:

 > Q: What prevents a CPU coming up -during- an MTRR change once the rest
 > of the cpu hot plugging is present ?

"The force". The more I think about mtrr.c and hotplug, the more I
regret having eaten lunch today.  I'm not convinced it will do the right
thing at all with hotplug. init_secondary_cpu() does no frobbing of
the MSRs. For this we relied upon that IPI from cpu #0, which we never
saw. Ugh. horrid.

So possible issues are..

1. cpu #0 sets MSRs, then sets off an IPI. cpu #n isn't 'plugged' yet,
   so we miss the IPI and new processors don't get the MSRs poked,
   but get their 'state' set so it appears to be ok, but isn't.
2. init on secondary cpu's probably needs to wait until the boot CPU mtrr
   code is in a 'known safe' state before it does the magickal
   'sync based on whats in cpu #0'
3. What happens when cpu #0 has finished poking registers, and then sets
   off an IPI to resync the others, when cpu #n hasn't gotten as far in the
   boot sequence to handle that IPI correctly yet ?

        Dave.

-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

Re: [PATCH] 2.5.25 Hotplug CPU boot changes

[Rusty Russell]

In message <1026736141.13885.105.camel@irongate.swansea.linux.org.uk> you write
:
> On Mon, 2002-07-15 at 09:58, Rusty Russell wrote:
> > The following patches change boot sequence, and once Linus releases
> > 2.5.26, I'll be updating and sending them.  This will break every SMP
> > architecture (patch for x86 below, and I have a patch for PPC32).
> >			printk("ksoftirqd for %i failedn", hotcpu);
> 
> Q: What prevents a CPU coming up -during- an MTRR change once the rest
> of the cpu hot plugging is present ?

Nothing, that's (one of the reasons) why cpu hotplug is not
implemented on x86.

[ Disclosure: I tried to rewrite the x86 boot code to actually bring
  CPUs up one at a time, rather than the minimal wedge seen in this
  patch, and failed.  Me no x86-pert, and the boot code is hairy. ]

I'm still considering a big reader lock around the actual bringing up
of CPUs, pending me completing my audit of what code actually needs
this (surprisingly, very little generic code actually cares how many
CPUs we have, so it's mainly a few corner cases).  This would be
cheap, and allow code that cared to lock out cpu changes.

Thoughts?
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.