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

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Message-ID: <20070427200247.GA7270@dreamland.darkstar.lan>
Date:	Fri, 27 Apr 2007 22:02:47 +0200
From:	Luca Tettamanti <kronos.it@...il.com>
To:	Miguel Ojeda <maxextreme@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	oliver pinter <oliver.pntr@...il.com>,
	Robert Hancock <hancockr@...w.ca>,
	Roman Zippel <zippel@...ux-m68k.org>
Subject: Re: [BUG? -rc7] SMP: Just one CPU activated: P4 3GHz HT

Il Mon, Apr 23, 2007 at 10:11:52AM +0200, Miguel Ojeda ha scritto: 
> On 4/22/07, Luca Tettamanti <kronos.it@...il.com> 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@...w.ca> 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@...pamshaw.ca
> >Home Page: http://www.roberthancock.com/
> >
> >
> 
> 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 <kronos.it@...il.com>
---

 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/i386/IO-APIC.txt>,
 	  <file:Documentation/nmi_watchdog.txt> and the SMP-HOWTO available at




Luca
-- 
"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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