Messages in this thread | | | Date | Sun, 15 Jan 2012 23:24:14 +0800 | From | Jiang Liu <> | Subject | Re: [PATCH v5 12/12] x86/topology.c: debug CPU0 hotplug |
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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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