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SubjectRe: [PATCH v5 12/12] x86/topology.c: debug CPU0 hotplug
On 01/12/2012 01:04 AM, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@intel.com>
>
> CONFIG_DEBUG_HOTPLUG_CPU0 is for debuging the CPU0 hotplug feature. The switch
> offlines CPU0 as soon as possible and boots userspace up with CPU0 offlined.
> User can online CPU0 back after boot time. The default value of the switch is
> off.
>
> To debug CPU0 hotplug, you need to enable CPU0 offline/online feature by either
> turning on CONFIG_BOOTPARAM_HOTPLUG_CPU0 during compilation or giving
> cpu0_hotplug kernel parameter at boot.
>
> It's safe and early place to take down CPU0 after all hotplug notifiers
> are installed and SMP is booted.
>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> ---
> arch/x86/Kconfig | 15 +++++++++++++++
> arch/x86/kernel/topology.c | 39 +++++++++++++++++++++++++++++++++++++++
> 2 files changed, 54 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index c2cf195..36b6a2c 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1748,6 +1748,21 @@ config BOOTPARAM_HOTPLUG_CPU0
> You still can enable the CPU0 hotplug feature at boot by kernel
> parameter cpu0_hotplug.
>
> +config DEBUG_HOTPLUG_CPU0
> + def_bool n
> + prompt "Debug CPU0 hotplug"
> + depends on HOTPLUG_CPU && EXPERIMENTAL
> + ---help---
> + Enabling this option offlines CPU0 (if CPU0 can be offlined) as
> + soon as possible and boots up userspace with CPU0 offlined. User
> + can online CPU0 back after boot time.
> +
> + To debug CPU0 hotplug, you need to enable CPU0 offline/online
> + feature by either turning on CONFIG_BOOTPARAM_HOTPLUG_CPU0 during
> + compilation or giving cpu0_hotplug kernel parameter at boot.
> +
> + If unuser, say N.
> +
> config COMPAT_VDSO
> def_bool y
> prompt "Compat VDSO support"
> diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
> index 8cec15c..3f697dd 100644
> --- a/arch/x86/kernel/topology.c
> +++ b/arch/x86/kernel/topology.c
> @@ -49,6 +49,45 @@ static int __init enable_cpu0_hotplug(char *str)
> __setup("cpu0_hotplug", enable_cpu0_hotplug);
> #endif
>
> +#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
> +/*
> + * This function offlines CPU0 as early as possible and allows userspace to
> + * boot up without CPU0. CPU0 can be onlined back by user after boot.
> + *
> + * This is only called for debugging CPU0 offline feature.
> + */
> +static void __init _debug_hotplug_cpu(int num)
> +{
> + int ret;
> + struct sys_device *dev = get_cpu_sysdev(num);
> +
> + /*
> + * Take hotpluggable online CPU0 down.
> + */
> + if (num || !per_cpu(cpu_devices, num).cpu.hotpluggable || !dev ||
> + !cpu_online(num)) {
> + pr_debug("CPU0 can't be offlined.\n");
> + return;
> + }
The usage of parameter num seems a little inconsistent.
Suggest either to remove the num parameter or to get rid of the assumption
that num is always zero.

> +
> + cpu_hotplug_driver_lock();
> +
> + ret = cpu_down(num);
> + if (!ret)
> + kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
> + else
> + pr_debug("Can't offline CPU%d.\n", num);
> +
> + cpu_hotplug_driver_unlock();
> +}
> +static int __init debug_hotplug_cpu(void)
> +{
> + _debug_hotplug_cpu(0);
> + return 0;
> +}
> +device_initcall_sync(debug_hotplug_cpu);
> +#endif /* CONFIG_DEBUG_HOTPLUG_CPU0 */
> +
> int __ref arch_register_cpu(int num)
> {
> /*



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