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| author | Fenghua Yu <fenghua.yu@intel.com> | 2012-11-13 20:32:51 +0100 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2012-11-15 00:28:11 +0100 |
| commit | a71c8bc5dfefbbf80ef90739791554ef7ea4401b (patch) | |
| tree | c45ca6284652a848876b2b2636c30a36111ec0b1 /arch/x86/include/asm/cpu.h | |
| parent | x86/i387.c: Initialize thread xstate only on CPU0 only once (diff) | |
| download | linux-a71c8bc5dfefbbf80ef90739791554ef7ea4401b.tar.xz linux-a71c8bc5dfefbbf80ef90739791554ef7ea4401b.zip | |
x86, topology: Debug CPU0 hotplug
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: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1352835171-3958-15-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/include/asm/cpu.h')
| -rw-r--r-- | arch/x86/include/asm/cpu.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h index a1195726e8c2..5f9a1243190e 100644 --- a/arch/x86/include/asm/cpu.h +++ b/arch/x86/include/asm/cpu.h @@ -29,6 +29,9 @@ struct x86_cpu { extern int arch_register_cpu(int num); extern void arch_unregister_cpu(int); extern void __cpuinit start_cpu0(void); +#ifdef CONFIG_DEBUG_HOTPLUG_CPU0 +extern int _debug_hotplug_cpu(int cpu, int action); +#endif #endif DECLARE_PER_CPU(int, cpu_state); |