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    SubjectRe: [rfc] fix Kconfig, hotplug_cpu is needed for swsusp
    Pavel Machek <pavel@ucw.cz> wrote:
    >
    > HOTPLUG_CPU is needed on normal PCs, too -- it is neccessary for
    > software suspend.
    >
    > Signed-off-by: Pavel Machek <pavel@suse.cz>
    >
    > ---
    > commit 2206dab43d50723d6b15caa8821e8d97c6b5ef28
    > tree cbfc324e15d216aa91ce6a51927668076de5b7db
    > parent dd76aabd03933b80c61fa5b0c0c995950246c603
    > author <pavel@amd.ucw.cz> Thu, 30 Mar 2006 00:06:31 +0200
    > committer <pavel@amd.ucw.cz> Thu, 30 Mar 2006 00:06:31 +0200
    >
    > arch/i386/Kconfig | 8 ++++----
    > kernel/power/process.c | 3 +--
    > kernel/signal.c | 1 +
    > 3 files changed, 6 insertions(+), 6 deletions(-)
    >
    > diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
    > index f7db71d..955dc08 100644
    > --- a/arch/i386/Kconfig
    > +++ b/arch/i386/Kconfig
    > @@ -741,12 +741,12 @@ config PHYSICAL_START
    >
    > config HOTPLUG_CPU
    > bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
    > - depends on SMP && HOTPLUG && EXPERIMENTAL && !X86_VOYAGER && !X86_PC
    > + depends on SMP && HOTPLUG && EXPERIMENTAL && !X86_VOYAGER
    > ---help---
    > - Say Y here to experiment with turning CPUs off and on. CPUs
    > - can be controlled through /sys/devices/system/cpu.
    > + Say Y here to experiment with turning CPUs off and on, and to
    > + enable suspend on SMP systems. CPUs can be controlled through
    > + /sys/devices/system/cpu.
    >
    > - Say N.
    >

    OK, this will get ugly. APICs are involved.

    That patch simply undoes this one:

    > [PATCH] x86: make CONFIG_HOTPLUG_CPU depend on !X86_PC
    >
    > Make CONFIG_HOTPLUG_CPU depend on !X86_PC, so we need to turn on either
    > CONFIG_GENERICARCH, CONFIG_BIGSMP or any other subarch except X86_PC when
    > CONFIG_HOTPLUG_CPU=y
    >
    > With 2.6.15+ kernels when CONFIG_HOTPLUG_CPU is turned on we switch to
    > bigsmp mode for sending IPI's and ioapic configurations that caused the
    > following error message.
    >
    > >> More than 8 CPUs detected and CONFIG_X86_PC cannot handle it.
    > >> Use CONFIG_X86_GENERICARCH or CONFIG_X86_BIGSMP.
    >
    > Originally bigsmp was added just to handle >8 cpus, but now with hotplug
    > cpu support we need to use bigsmp mode (why? see below), that cause the
    > above error message even if there were less than 8 cpus in the system.
    >
    > The message is bogus, but we are cannot use logical flat mode due to issues
    > with broadcast IPI can confuse a CPU just comming up. We use flat physical
    > mode just like x86_64 case. More details on why bigsmp now uses flat
    > physical mode (vs. cluster mode) in following link.
    >
    > http://marc.theaimsgroup.com/?l=linux-kernel&m=113261865814107&w=2
    >

    Which I was distinctly uncomfortable with. (And glad I nixed it for 2.6.16 ;))

    Ashok, we need to do something better, but what?
    -
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