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authorFenghua Yu <fenghua.yu@intel.com>2012-11-13 11:32:38 -0800
committerH. Peter Anvin <hpa@linux.intel.com>2012-11-14 09:39:44 -0800
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parent77b67063bb6bce6d475e910d3b886a606d0d91f7 (diff)
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doc: Add x86 CPU0 online/offline feature
If CONFIG_BOOTPARAM_HOTPLUG_CPU0 is turned on, CPU0 is hotpluggable. Otherwise, by default CPU0 is not hotpluggable and kernel parameter cpu0_hotplug enables CPU0 online/offline feature. The documentations point out two known CPU0 dependencies. First, resume from hibernate or suspend always starts from CPU0. So hibernate and suspend are prevented if CPU0 is offline. Another dependency is PIC interrupts always go to CPU0. It's said that some machines may depend on CPU0 to poweroff/reboot. But I haven't seen such dependency on a few tested machines. Please let me know if you see any CPU0 dependencies on your machine. Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> Link: http://lkml.kernel.org/r/1352835171-3958-2-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
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diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
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--- a/Documentation/kernel-parameters.txt
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@@ -1984,6 +1984,20 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
nox2apic [X86-64,APIC] Do not enable x2APIC mode.
+ cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
+ CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
+ Some features depend on CPU0. Known dependencies are:
+ 1. Resume from suspend/hibernate depends on CPU0.
+ Suspend/hibernate will fail if CPU0 is offline and you
+ need to online CPU0 before suspend/hibernate.
+ 2. PIC interrupts also depend on CPU0. CPU0 can't be
+ removed if a PIC interrupt is detected.
+ It's said poweroff/reboot may depend on CPU0 on some
+ machines although I haven't seen such issues so far
+ after CPU0 is offline on a few tested machines.
+ If the dependencies are under your control, you can
+ turn on cpu0_hotplug.
+
nptcg= [IA-64] Override max number of concurrent global TLB
purges which is reported from either PAL_VM_SUMMARY or
SAL PALO.
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