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Subject[patch 2/5] x86_64: CPU hotplug support.
Experimental CPU hotplug patch for x86_64
-----------------------------------------
This supports logical CPU online and offline.
- Test with maxcpus=1, and then kick other cpu's off to test if init code
is all cleaned up. CONFIG_SCHED_SMT works as well.
- idle threads are forked on demand from keventd threads for clean startup

TBD:
1. Not tested on a real NUMA machine (tested with numa=fake=2)
2. Handle ACPI pieces for physical hotplug support.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
-----------------------------------------

arch/i386/mach-default/topology.c | 15 +-
arch/x86_64/Kconfig | 9 +
arch/x86_64/kernel/irq.c | 30 +++++
arch/x86_64/kernel/process.c | 29 +++++
arch/x86_64/kernel/smp.c | 12 ++
arch/x86_64/kernel/smpboot.c | 201 ++++++++++++++++++++++++++++++++++----
arch/x86_64/kernel/traps.c | 8 +
include/asm-x86_64/irq.h | 5
include/asm-x86_64/smp.h | 4
9 files changed, 286 insertions(+), 27 deletions(-)

Index: linux-2.6.12-rc5-mm2/arch/x86_64/Kconfig
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/Kconfig
+++ linux-2.6.12-rc5-mm2/arch/x86_64/Kconfig
@@ -288,6 +288,15 @@ config NR_CPUS
This is purely to save memory - each supported CPU requires
memory in the static kernel configuration.

+config HOTPLUG_CPU
+ bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
+ depends on SMP && HOTPLUG && EXPERIMENTAL
+ help
+ Say Y here to experiment with turning CPUs off and on. CPUs
+ can be controlled through /sys/devices/system/cpu/cpu#.
+ Say N if you want to disable CPU hotplug.
+
+
config HPET_TIMER
bool
default y
Index: linux-2.6.12-rc5-mm2/arch/x86_64/kernel/smpboot.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/kernel/smpboot.c
+++ linux-2.6.12-rc5-mm2/arch/x86_64/kernel/smpboot.c
@@ -34,6 +34,7 @@
* Andi Kleen : Converted to new state machine.
* Various cleanups.
* Probably mostly hotplug CPU ready now.
+ * Ashok Raj : CPU hotplug support
*/


@@ -98,6 +99,37 @@ EXPORT_SYMBOL(cpu_core_map);
extern unsigned char trampoline_data[];
extern unsigned char trampoline_end[];

+/* State of each CPU */
+DEFINE_PER_CPU(int, cpu_state) = { 0 };
+
+/*
+ * Store all idle threads, this can be reused instead of creating
+ * a new thread. Also avoids complicated thread destroy functionality
+ * for idle threads.
+ */
+struct task_struct *idle_thread_array[NR_CPUS] __cpuinitdata ;
+
+#define get_idle_for_cpu(x) (idle_thread_array[(x)])
+#define set_idle_for_cpu(x,p) (idle_thread_array[(x)] = (p))
+
+/*
+ * cpu_possible_map should be static, it cannot change as cpu's
+ * are onlined, or offlined. The reason is per-cpu data-structures
+ * are allocated by some modules at init time, and dont expect to
+ * do this dynamically on cpu arrival/departure.
+ * cpu_present_map on the other hand can change dynamically.
+ * In case when cpu_hotplug is not compiled, then we resort to current
+ * behaviour, which is cpu_possible == cpu_present.
+ * If cpu-hotplug is supported, then we need to preallocate for all
+ * those NR_CPUS, hence cpu_possible_map represents entire NR_CPUS range.
+ * - Ashok Raj
+ */
+#ifdef CONFIG_HOTPLUG_CPU
+#define fixup_cpu_possible_map(x) cpu_set((x), cpu_possible_map)
+#else
+#define fixup_cpu_possible_map(x)
+#endif
+
/*
* Currently trivial. Write the real->protected mode
* bootstrap into the page concerned. The caller
@@ -445,8 +477,10 @@ void __cpuinit start_secondary(void)
/*
* Allow the master to continue.
*/
+ lock_ipi_call_lock();
cpu_set(smp_processor_id(), cpu_online_map);
mb();
+ unlock_ipi_call_lock();

/* Wait for TSC sync to not schedule things before.
We still process interrupts, which could see an inconsistent
@@ -623,33 +657,67 @@ static int __cpuinit wakeup_secondary_vi
return (send_status | accept_status);
}

+struct create_idle {
+ struct task_struct *idle;
+ struct completion done;
+ int cpu;
+};
+
+void do_fork_idle(void *_c_idle)
+{
+ struct create_idle *c_idle = _c_idle;
+
+ c_idle->idle = fork_idle(c_idle->cpu);
+ complete(&c_idle->done);
+}
+
/*
* Boot one CPU.
*/
static int __cpuinit do_boot_cpu(int cpu, int apicid)
{
- struct task_struct *idle;
unsigned long boot_error;
int timeout;
unsigned long start_rip;
- /*
- * We can't use kernel_thread since we must avoid to
- * reschedule the child.
- */
- idle = fork_idle(cpu);
- if (IS_ERR(idle)) {
+ struct create_idle c_idle = {
+ .cpu = cpu,
+ .done = COMPLETION_INITIALIZER(c_idle.done),
+ };
+ DECLARE_WORK(work, do_fork_idle, &c_idle);
+
+ c_idle.idle = get_idle_for_cpu(cpu);
+
+ if (c_idle.idle) {
+ c_idle.idle->thread.rsp = (unsigned long) (((struct pt_regs *)
+ (THREAD_SIZE + (unsigned long) c_idle.idle->thread_info)) - 1);
+ init_idle(c_idle.idle, cpu);
+ goto do_rest;
+ }
+
+ if (!keventd_up() || current_is_keventd())
+ work.func(work.data);
+ else {
+ schedule_work(&work);
+ wait_for_completion(&c_idle.done);
+ }
+
+ if (IS_ERR(c_idle.idle)) {
printk("failed fork for CPU %d\n", cpu);
- return PTR_ERR(idle);
+ return PTR_ERR(c_idle.idle);
}

- cpu_pda[cpu].pcurrent = idle;
+ set_idle_for_cpu(cpu, c_idle.idle);
+
+do_rest:
+
+ cpu_pda[cpu].pcurrent = c_idle.idle;

start_rip = setup_trampoline();

- init_rsp = idle->thread.rsp;
+ init_rsp = c_idle.idle->thread.rsp;
per_cpu(init_tss,cpu).rsp0 = init_rsp;
initial_code = start_secondary;
- clear_ti_thread_flag(idle->thread_info, TIF_FORK);
+ clear_ti_thread_flag(c_idle.idle->thread_info, TIF_FORK);

printk(KERN_INFO "Booting processor %d/%d rip %lx rsp %lx\n", cpu, apicid,
start_rip, init_rsp);
@@ -925,10 +993,9 @@ void __init smp_prepare_cpus(unsigned in
int apicid = cpu_present_to_apicid(i);
if (physid_isset(apicid, phys_cpu_present_map)) {
cpu_set(i, cpu_present_map);
- /* possible map would be different if we supported real
- CPU hotplug. */
cpu_set(i, cpu_possible_map);
}
+ fixup_cpu_possible_map(i);
}

if (smp_sanity_check(max_cpus) < 0) {
@@ -977,9 +1044,6 @@ void __init smp_prepare_boot_cpu(void)

/*
* Entry point to boot a CPU.
- *
- * This is all __cpuinit, not __devinit for now because we don't support
- * CPU hotplug (yet).
*/
int __cpuinit __cpu_up(unsigned int cpu)
{
@@ -996,6 +1060,14 @@ int __cpuinit __cpu_up(unsigned int cpu)
return -EINVAL;
}

+ /*
+ * Already booted CPU?
+ */
+ if (cpu_isset(cpu, cpu_callin_map)) {
+ Dprintk ("do_boot_cpu %d Already started\n", cpu);
+ return -ENOSYS;
+ }
+
/* Boot it! */
err = do_boot_cpu(cpu, apicid);
if (err < 0) {
@@ -1008,7 +1080,9 @@ int __cpuinit __cpu_up(unsigned int cpu)

while (!cpu_isset(cpu, cpu_online_map))
cpu_relax();
- return 0;
+ err = 0;
+
+ return err;
}

/*
@@ -1016,7 +1090,9 @@ int __cpuinit __cpu_up(unsigned int cpu)
*/
void __init smp_cpus_done(unsigned int max_cpus)
{
+#ifndef CONFIG_HOTPLUG_CPU
zap_low_mappings();
+#endif
smp_cleanup_boot();

#ifdef CONFIG_X86_IO_APIC
@@ -1028,3 +1104,94 @@ void __init smp_cpus_done(unsigned int m

check_nmi_watchdog();
}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+static void
+remove_siblinginfo(int cpu)
+{
+ int sibling;
+
+ for_each_cpu_mask(sibling, cpu_sibling_map[cpu])
+ cpu_clear(cpu, cpu_sibling_map[sibling]);
+ for_each_cpu_mask(sibling, cpu_core_map[cpu])
+ cpu_clear(cpu, cpu_core_map[sibling]);
+ cpus_clear(cpu_sibling_map[cpu]);
+ cpus_clear(cpu_core_map[cpu]);
+ phys_proc_id[cpu] = BAD_APICID;
+ cpu_core_id[cpu] = BAD_APICID;
+}
+
+void remove_cpu_from_maps(void)
+{
+ int cpu = smp_processor_id();
+
+ cpu_clear(cpu, cpu_callout_map);
+ cpu_clear(cpu, cpu_callin_map);
+ clear_bit(cpu, &cpu_initialized); /* was set by cpu_init() */
+}
+
+int __cpu_disable(void)
+{
+ int cpu = smp_processor_id();
+
+ /*
+ * Perhaps use cpufreq to drop frequency, but that could go
+ * into generic code.
+ *
+ * We won't take down the boot processor on i386 due to some
+ * interrupts only being able to be serviced by the BSP.
+ * Especially so if we're not using an IOAPIC -zwane
+ */
+ if (cpu == 0)
+ return -EBUSY;
+
+ disable_APIC_timer();
+
+ /*
+ * HACK:
+ * Allow any queued timer interrupts to get serviced
+ * This is only a temporary solution until we cleanup
+ * fixup_irqs as we do for IA64.
+ */
+ local_irq_enable();
+ mdelay(1);
+
+ local_irq_disable();
+ remove_siblinginfo(cpu);
+
+ /* It's now safe to remove this processor from the online map */
+ cpu_clear(cpu, cpu_online_map);
+ remove_cpu_from_maps();
+ fixup_irqs(cpu_online_map);
+ return 0;
+}
+
+void __cpu_die(unsigned int cpu)
+{
+ /* We don't do anything here: idle task is faking death itself. */
+ unsigned int i;
+
+ for (i = 0; i < 10; i++) {
+ /* They ack this in play_dead by setting CPU_DEAD */
+ if (per_cpu(cpu_state, cpu) == CPU_DEAD)
+ return;
+ current->state = TASK_UNINTERRUPTIBLE;
+ schedule_timeout(HZ/10);
+ }
+ printk(KERN_ERR "CPU %u didn't die...\n", cpu);
+}
+
+#else /* ... !CONFIG_HOTPLUG_CPU */
+
+int __cpu_disable(void)
+{
+ return -ENOSYS;
+}
+
+void __cpu_die(unsigned int cpu)
+{
+ /* We said "no" in __cpu_disable */
+ BUG();
+}
+#endif /* CONFIG_HOTPLUG_CPU */
Index: linux-2.6.12-rc5-mm2/arch/x86_64/kernel/irq.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/kernel/irq.c
+++ linux-2.6.12-rc5-mm2/arch/x86_64/kernel/irq.c
@@ -14,6 +14,7 @@
#include <linux/interrupt.h>
#include <linux/seq_file.h>
#include <linux/module.h>
+#include <linux/delay.h>
#include <asm/uaccess.h>
#include <asm/io_apic.h>

@@ -106,3 +107,32 @@ asmlinkage unsigned int do_IRQ(struct pt

return 1;
}
+
+#ifdef CONFIG_HOTPLUG_CPU
+void fixup_irqs(cpumask_t map)
+{
+ unsigned int irq;
+ static int warned;
+
+ for (irq = 0; irq < NR_IRQS; irq++) {
+ cpumask_t mask;
+ if (irq == 2)
+ continue;
+
+ cpus_and(mask, irq_affinity[irq], map);
+ if (any_online_cpu(mask) == NR_CPUS) {
+ printk("Breaking affinity for irq %i\n", irq);
+ mask = map;
+ }
+ if (irq_desc[irq].handler->set_affinity)
+ irq_desc[irq].handler->set_affinity(irq, mask);
+ else if (irq_desc[irq].action && !(warned++))
+ printk("Cannot set affinity for irq %i\n", irq);
+ }
+
+ /* That doesn't seem sufficient. Give it 1ms. */
+ local_irq_enable();
+ mdelay(1);
+ local_irq_disable();
+}
+#endif
Index: linux-2.6.12-rc5-mm2/include/asm-x86_64/irq.h
===================================================================
--- linux-2.6.12-rc5-mm2.orig/include/asm-x86_64/irq.h
+++ linux-2.6.12-rc5-mm2/include/asm-x86_64/irq.h
@@ -52,4 +52,9 @@ struct irqaction;
struct pt_regs;
int handle_IRQ_event(unsigned int, struct pt_regs *, struct irqaction *);

+#ifdef CONFIG_HOTPLUG_CPU
+#include <linux/cpumask.h>
+extern void fixup_irqs(cpumask_t map);
+#endif
+
#endif /* _ASM_IRQ_H */
Index: linux-2.6.12-rc5-mm2/arch/x86_64/kernel/process.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/kernel/process.c
+++ linux-2.6.12-rc5-mm2/arch/x86_64/kernel/process.c
@@ -8,7 +8,8 @@
*
* X86-64 port
* Andi Kleen.
- *
+ *
+ * CPU hotplug support - ashok.raj@intel.com
* $Id: process.c,v 1.38 2002/01/15 10:08:03 ak Exp $
*/

@@ -18,6 +19,7 @@

#include <stdarg.h>

+#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
@@ -154,6 +156,29 @@ void cpu_idle_wait(void)
}
EXPORT_SYMBOL_GPL(cpu_idle_wait);

+#ifdef CONFIG_HOTPLUG_CPU
+DECLARE_PER_CPU(int, cpu_state);
+
+#include <asm/nmi.h>
+/* We don't actually take CPU down, just spin without interrupts. */
+static inline void play_dead(void)
+{
+ idle_task_exit();
+ mb();
+ /* Ack it */
+ __get_cpu_var(cpu_state) = CPU_DEAD;
+
+ local_irq_disable();
+ while (1)
+ safe_halt();
+}
+#else
+static inline void play_dead(void)
+{
+ BUG();
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
/*
* The idle thread. There's no useful work to be
* done, so just try to conserve power and have a
@@ -174,6 +199,8 @@ void cpu_idle (void)
idle = pm_idle;
if (!idle)
idle = default_idle;
+ if (cpu_is_offline(smp_processor_id()))
+ play_dead();
idle();
}

Index: linux-2.6.12-rc5-mm2/include/asm-x86_64/smp.h
===================================================================
--- linux-2.6.12-rc5-mm2.orig/include/asm-x86_64/smp.h
+++ linux-2.6.12-rc5-mm2/include/asm-x86_64/smp.h
@@ -44,6 +44,8 @@ extern void smp_alloc_memory(void);
extern volatile unsigned long smp_invalidate_needed;
extern int pic_mode;
extern int smp_num_siblings;
+extern void lock_ipi_call_lock(void);
+extern void unlock_ipi_call_lock(void);
extern void smp_flush_tlb(void);
extern void smp_message_irq(int cpl, void *dev_id, struct pt_regs *regs);
extern void smp_send_reschedule(int cpu);
@@ -77,6 +79,8 @@ extern __inline int hard_smp_processor_i
}

extern int safe_smp_processor_id(void);
+extern int __cpu_disable(void);
+extern void __cpu_die(unsigned int cpu);

#endif /* !ASSEMBLY */

Index: linux-2.6.12-rc5-mm2/arch/x86_64/kernel/traps.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/kernel/traps.c
+++ linux-2.6.12-rc5-mm2/arch/x86_64/kernel/traps.c
@@ -589,11 +589,17 @@ static void unknown_nmi_error(unsigned c
asmlinkage void default_do_nmi(struct pt_regs *regs)
{
unsigned char reason = 0;
+ int cpu;
+
+ cpu = smp_processor_id();

/* Only the BSP gets external NMIs from the system. */
- if (!smp_processor_id())
+ if (!cpu)
reason = get_nmi_reason();

+ if (!cpu_online(cpu))
+ return;
+
if (!(reason & 0xc0)) {
if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, reason, 0, SIGINT)
== NOTIFY_STOP)
Index: linux-2.6.12-rc5-mm2/arch/x86_64/kernel/smp.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/x86_64/kernel/smp.c
+++ linux-2.6.12-rc5-mm2/arch/x86_64/kernel/smp.c
@@ -295,6 +295,18 @@ struct call_data_struct {

static struct call_data_struct * call_data;

+void
+lock_ipi_call_lock(void)
+{
+ spin_lock_irq(&call_lock);
+}
+
+void
+unlock_ipi_call_lock(void)
+{
+ spin_unlock_irq(&call_lock);
+}
+
/*
* this function sends a 'generic call function' IPI to all other CPUs
* in the system.
Index: linux-2.6.12-rc5-mm2/arch/i386/mach-default/topology.c
===================================================================
--- linux-2.6.12-rc5-mm2.orig/arch/i386/mach-default/topology.c
+++ linux-2.6.12-rc5-mm2/arch/i386/mach-default/topology.c
@@ -73,12 +73,11 @@ static int __init topology_init(void)
{
int i;

- for (i = 0; i < MAX_NUMNODES; i++) {
- if (node_online(i))
- arch_register_node(i);
- }
- for (i = 0; i < NR_CPUS; i++)
- if (cpu_possible(i)) arch_register_cpu(i);
+ for_each_online_node(i)
+ arch_register_node(i);
+
+ for_each_cpu(i)
+ arch_register_cpu(i);
return 0;
}

@@ -88,8 +87,8 @@ static int __init topology_init(void)
{
int i;

- for (i = 0; i < NR_CPUS; i++)
- if (cpu_possible(i)) arch_register_cpu(i);
+ for_each_cpu(i)
+ arch_register_cpu(i);
return 0;
}

--

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