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    SubjectRe: [PATCH v3 5/7] Documentations/cpu-hotplug.tx, kernel-parameters.txt: Add x86 CPU0 online/offline feature
    On Wed, Nov 09, 2011 at 04:34:15PM -0800, Fenghua Yu wrote:
    > From: Fenghua Yu <fenghua.yu@intel.com>
    >
    > Add x86 CPU0 online/offline feature in the two documentations.
    >
    > By default BSP is not pluggable. Kernel parameter bsp_hotplug enables BSP
    > online/offline feature.
    >
    > The documentations point out two BSP dependencies. First, resume from hibernate
    > or suspend always starts from BSP. So hibernate and suspend are prevented if BSP
    > is offline. Another dependency is PIC interrupts always go to BSP.
    >
    > 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>
    > ---
    > ---
    > Documentation/cpu-hotplug.txt | 19 +++++++++++++++++++
    > Documentation/kernel-parameters.txt | 13 +++++++++++++
    > 2 files changed, 32 insertions(+), 0 deletions(-)
    >
    > diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
    > index a20bfd4..93af1a0 100644
    > --- a/Documentation/cpu-hotplug.txt
    > +++ b/Documentation/cpu-hotplug.txt
    > @@ -207,6 +207,25 @@ by making it not-removable.
    >
    > In such cases you will also notice that the online file is missing under cpu0.
    >
    > +Q: Is CPU0 removable on X86?
    > +A: Yes. If given kernel option bsp_hotplug, CPU0 is removable.
    > +
    > +But some features depend on BSP. Known dependencies are:
    > +1. Resume from hibernate/suspend depends on BSP. Hibernate/suspend will fail if
    > +BSP is offline and you need to online BSP before hibernate/suspend can continue.
    > +2. PIC interrupts also depend on BSP. BSP can't be removed if a PIC interrupt
    > +is detected.
    > +
    > +It's said poweroff/reboot may depend on BSP on some machines although I haven't
    > +seen any poweroff/reboot failure so far after BSP is offline on a few tested
    > +machines.
    > +
    > +Please let me know if you know or see any other dependencies of BSP.

    You should include your email so folks can contact you.

    > +
    > +If the dependencies are under your control, you can turn on bsp_hotplug.
    > +
    > +--Fenghua Yu
    > +
    > Q: How do i find out if a particular CPU is not removable?
    > A: Depending on the implementation, some architectures may show this by the
    > absence of the "online" file. This is done if it can be determined ahead of
    > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    > index a0c5c5f..55582db 100644
    > --- a/Documentation/kernel-parameters.txt
    > +++ b/Documentation/kernel-parameters.txt
    > @@ -1842,6 +1842,19 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
    >
    > nox2apic [X86-64,APIC] Do not enable x2APIC mode.
    >
    > + bsp_hotplug [X86] BSP (aka CPU0) is hotpluggable.
    > + Some features depend on BSP. Known dependencies are:
    > + 1. Resume from suspend/hibernate depends on BSP.
    > + Suspend/hibernate will fail if BSP is offline and you
    > + need to online BSP before suspend/hibernate.
    > + 2. PIC interrupts also depend on BSP. BSP can't be
    > + removed if a PIC interrupt is detected.
    > + It's said poweroff/reboot may depend on BSP on some
    > + machines although I haven't seen such issues so far
    > + after BSP is offline on a few tested machines.
    > + If the dependencies are under your control, you can
    > + turn on bsp_hotplug.
    > +
    > nptcg= [IA-64] Override max number of concurrent global TLB
    > purges which is reported from either PAL_VM_SUMMARY or
    > SAL PALO.
    > --
    > 1.6.0.3
    >
    > --
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