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    SubjectRe: [PATCH 6/8] x86, topology.c: Enable CPU0 online/offline
    On Wed, 5 Oct 2011, Fenghua Yu wrote:

    > From: Fenghua Yu <fenghua.yu@intel.com>
    >
    > Enable CPU0 online/offline by setting up its sysfs control file. By default,
    > this feature is disabled. You can enabled it by bsp_hotplug kernel option.
    >
    > Resume from hibernate, standby, or suspend needs CPU0 online. According to
    > arch/x86/kernel/topology.c, some PCI quirks(??) need CPU0 online as well. Anyone
    > knows which PCI quirks depends on CPU0 online?
    >
    > Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
    > ---
    > Documentation/kernel-parameters.txt | 7 +++++++
    > arch/x86/kernel/topology.c | 22 +++++++++++++++-------
    > 2 files changed, 22 insertions(+), 7 deletions(-)
    >
    > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    > index 854ed5c..bf011ee 100644
    > --- a/Documentation/kernel-parameters.txt
    > +++ b/Documentation/kernel-parameters.txt
    > @@ -1805,6 +1805,13 @@ 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.
    > + Suspend/resume depends on BSP. It's said some PCI
    > + quirks depend on BSP too. But not sure which quirks.

    Right, not sure what breaks. Go ahead and watch your machine explode.

    > + If don't care the dependencies, you can turn on
    > + bsp_ hotplug. Suspend will fail if BSP is offlined and
    > + you need to online BSP before suspend/resume.

    And you forgot poweroff and reboot, which have similar dependencies on
    some machines. That whole low level ACPI stuff is sensitive.

    > +
    > nptcg= [IA-64] Override max number of concurrent global TLB
    > purges which is reported from either PAL_VM_SUMMARY or
    > SAL PALO.
    > diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
    > index 8927486..ed2da5c 100644
    > --- a/arch/x86/kernel/topology.c
    > +++ b/arch/x86/kernel/topology.c
    > @@ -34,18 +34,26 @@
    > static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
    >
    > #ifdef CONFIG_HOTPLUG_CPU
    > +
    > +static int __init enable_bsp_hotplug(char *str)
    > +{
    > + bsp_hotpluggable = 1;

    And that variable is defined where? I know where in the following
    patch, so it's clear that series was neither compiled step per step
    nor booted.

    > + * Suspend/resume depends on BSP. Certain PCI quirks (which PCI
    > + * quirks??) require not to enable hotplug control for all CPU's.

    Again, you dammit better make shure which quirks break when cpu0 is
    offlined.

    Thanks,

    tglx


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