• Fenghua Yu's avatar
    x86, topology: Debug CPU0 hotplug · a71c8bc5
    Fenghua Yu authored
    CONFIG_DEBUG_HOTPLUG_CPU0 is for debugging 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.
    
    Please note that some applications or drivers, e.g. some versions of udevd,
    during boot time may put CPU0 online again in this CPU0 hotplug debug mode.
    
    In this debug mode, setup_local_APIC() may report a warning on max_loops<=0
    when CPU0 is onlined back after boot time. This is because pending interrupt in
    IRR can not move to ISR. The warning is not CPU0 specfic and it can happen on
    other CPUs as well. It is harmless except the first CPU0 online takes a bit
    longer time. And so this debug mode is useful to expose this issue. I'll send
    a seperate patch to fix this generic warning issue.
    Signed-off-by: default avatarFenghua Yu <fenghua.yu@intel.com>
    Link: http://lkml.kernel.org/r/1352835171-3958-15-git-send-email-fenghua.yu@intel.comSigned-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
    a71c8bc5
topology.c 4.04 KB