Re: [BUG? -rc7] SMP: Just one CPU activated: P4 3GHz HT

From: Luca Tettamanti
Date: Fri Apr 27 2007 - 16:03:18 EST

Il Mon, Apr 23, 2007 at 10:11:52AM +0200, Miguel Ojeda ha scritto:
> On 4/22/07, Luca Tettamanti <> wrote:
> >Probably the two siblings are enumerated only in ACPI tables. If you
> >disable ACPI the kernel won't be aware of the second "core".
> >
> >Luca
> >--
> >"Su cio` di cui non si puo` parlare e` bene tacere".
> > Ludwig Wittgenstein
> >
> On 4/23/07, Robert Hancock <hancockr@xxxxxxx> wrote:
> >
> >You didn't enable ACPI, it's needed for almost all systems to detect HT
> >and also for many systems to detect multi-cores as well.
> >
> >Aside from that, in general I would say that on any modern x86 system
> >ACPI should always be enabled. In many cases it seems the BIOS code is
> >not tested much without ACPI anymore, so going without ACPI can be
> >problematic.
> >
> >--
> >Robert Hancock Saskatoon, SK, Canada
> >To email, remove "nospam" from hancockr@xxxxxxxxxxxxx
> >Home Page:
> >
> >
> Thanks all of you. It seems the problem is ACPI, however, should not
> it be noted in some way? Maybe at Documentation/smp.txt, maybe at the
> help section at CONFIG_SMP, maybe a "depends on ..."
> Or maybe CONFIG_SMP should enable some bits of the ACPI code needed to
> detect such additional cores.

"depends on" is too strong. There exists architecture without ACPI but
with SMP support; even in the x86 world a number of systems still
support both MPS and ACPI.

Mentioning it in the help text should be enough. Roman, are you in
charge for the KConfig files?

SMP support in modern systems often relies on ACPI being active; add a
couple of lines in the help text for CONFIG_SMP

Signed-Off-By: Luca Tettamanti <>

arch/i386/Kconfig | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index 53d6237..48ef899 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -111,6 +111,9 @@ config SMP
Y to "Enhanced Real Time Clock Support", below. The "Advanced Power
Management" code will be disabled if you say Y here.

+ Note that ACPI is often required to support newer multi-core CPUs
+ and HT on Intel P4 processors.
See also the <file:Documentation/smp.txt>,
<file:Documentation/nmi_watchdog.txt> and the SMP-HOWTO available at

"Vorrei morire ucciso dagli agi. Vorrei che di me si dicesse: ``Com'è
morto?'' ``Gli è scoppiato il portafogli''" -- Marcello Marchesi
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