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Re: Disabling ACPI also implicitly disables SMP support for Intel Atom chips?

On Wed, 4 Mar 2009 23:58:26 +0000, Andrew Doran wrote:
From: Andrew Doran <>
To: "Jared D. McNeill" <>
CC: "David H. Gutteridge" <>, Subject: Re: Disabling ACPI also implicitly disables SMP support for Intel Atom chips?
Date: Wed, 4 Mar 2009 23:58:26 +0000

On Wed, Mar 04, 2009 at 05:18:23PM -0500, Jared D. McNeill wrote:
> David H. Gutteridge wrote:
> >Hi all,
> >
> >Is it a given that disabling ACPI also disables SMP (well, really SMT,
> >technically) with Intel Atom chips?  (Or others?)  The i386 boot prompt
> >offers the choice of disabling ACPI only, but when I choose it on my
> >LG X110 netbook, the kernel doesn't recognize the HT capabilities of
> >the CPU.  In order to get SMP, I have to enable ACPI.  Is this
> >something I should PR, or is it just the nature of things here?  (This
> >is with 5.0 RC2, incidentally.)
> Does your motherboard have MP BIOS extensions (the fallback when ACPI
> isn't enabled)? I suspect not.

I have found that the trend is to report HT via ACPI but not via MPBIOS.
Dual cores tend to show up via MPBIOS.

David, what's the issue with ACPI?


Hi Andrew,

The main problem I've found so far with ACPI being enabled (I've only
been using this machine a few days) is that the Ethernet card doesn't
work.  With ACPI, the card doesn't seem to transmit any packets, and
every few seconds I see the following output to the console:

re0: watchdog timeout
re0: reset never completed!

If I disable ACPI, the re(4) card works fine.  (Well, except for
hardware checksumming, but that's a minor issue.)  So at present, I
have to choose between better performance for intensive work like
compiles (corresponding with those benchmarks you'd asked for on tech-
kern a month ago, I found building a kernel for instance is about 20%
faster with HT enabled), or networking.  (I don't mean to sound
facetious, I have used both of those choices, I can live without
networking a lot of the time, given what I'm using this machine for.
Obviously it'd be nice not to have to choose.)  I was going to PR this,
but I hadn't gotten around to it yet, I certainly can.

The other thing I've noticed is that the brightness keys work if ACPI
is disabled, but they don't work if it's enabled.  (That seems odd to
me, but I'm no expert at these things.)



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