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SubjectRe: More than 8 CPUs detected and CONFIG_X86_PC cannot handle it on 2.6.16-rc6
Ashok Raj <> 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 <>
> ---------------------------------------------------------
> 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

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

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