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    SubjectRe: More than 8 CPUs detected and CONFIG_X86_PC cannot handle it on 2.6.16-rc6
    Ashok Raj <ashok.raj@intel.com> wrote:
    >
    >
    >
    > When CONFIG_HOTPLUG_CPU is turned on we always use physflat mode (bigsmp) even
    > when #of CPUs are less than 8 to avoid sending IPI to offline processors.
    >
    > Without having BIGSMP on it spits out a warning during boot on systems that
    > seems misleading, since it complains even on systems that have less
    > than 8 cpus.
    >
    > Signed-off-by: Ashok Raj <ashok.raj@intel.com>
    > ---------------------------------------------------------
    >
    > arch/i386/Kconfig | 2 +-
    > 1 files changed, 1 insertion(+), 1 deletion(-)
    >
    > Index: linux-2.6.16-rc6-mm1/arch/i386/Kconfig
    > ===================================================================
    > --- linux-2.6.16-rc6-mm1.orig/arch/i386/Kconfig
    > +++ linux-2.6.16-rc6-mm1/arch/i386/Kconfig
    > @@ -760,7 +760,7 @@ config PHYSICAL_START
    >
    > config HOTPLUG_CPU
    > bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
    > - depends on SMP && HOTPLUG && EXPERIMENTAL && !X86_VOYAGER
    > + depends on SMP && HOTPLUG && EXPERIMENTAL && !X86_VOYAGER && !X86_PC
    > ---help---
    > Say Y here to experiment with turning CPUs off and on. CPUs
    > can be controlled through /sys/devices/system/cpu.

    Still seems wrong. People _do_ use HOTPLUG_CPU on X86_PCs so they can get
    software suspend. The number of people who do this are probably 100000x
    the number of people who have physically hotpluggable CPUs. And I don't
    think we can churn their config requirements this much so late in the game.

    So for now I suggest we're best off simply killing the printk (or doing
    something smarter, like comparing cpu_online-map with cpu_possible_map
    (which isn't right)).

    Longer term, it appears that we need to do some Kconfig and C work to
    separate out the HOTPLUG_CPU infrastructure which swsusp needs from actual
    CPU hotplugging.

    What _is_ this IPI problem anyway? Can't send point-to-point IPIs to
    offlined CPUs? (Don't do that then?) Or do broadcast IPIs go wrong, or
    what?

    And does it affect pretend-x86-hotplug, or is it only affecting real hotplug?

    Thanks.
    -
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