Re: turning off APIC

Re: turning off APIC

[Mikael Pettersson]

On Sun, 15 Sep 2002 14:28:44 +0300, Andriy Rysin wrote:
>If APIC is compiled in the kernel (wich is the case with most 
>distributions) when I start kernel with "noapic" option, APIC is getting 
>enabled anyway and only later gets disabled. This causes problems on 
>some VAIO notebooks - it seems like BIOS gets confused if APIC was 
>turned on (particularly on my laptop when I try to reboot from Linux it 
>hangs saying that thera problems with keyboard). That would be much 
>better to have an option to turn it off in the boot options and not to 
>recompile the kernel. Could somebody comment this please?
>Please CC me on this email address.

Which APIC? local or I/O? Please be specific.
"noapic" does not and never has had anything to do with the
local APIC, only the I/O APIC. There is currently no kernel
option for preventing the local APIC from being enabled if
the kernel was built with local APIC support.

You have four options:
1. Recompile with CONFIG_SMP=n and CONFIG_X86_LOCAL_APIC=n.
2. Run dmidecode on your Vaio, dig out the identification strings,
   and add them to arch/i386/kernel/dmi_scan.c's local APIC
   blacklist.
3. Add a __setup in arch/i386/kernel/apic.c after the declaration
   for dont_enable_local_apic, which sets it to 1.
4. Tell Sony to fix the Vaio's BIOS.

/Mikael

Re: turning off APIC

[Maciej W. Rozycki]

On Mon, 16 Sep 2002, Mikael Pettersson wrote:

> Which APIC? local or I/O? Please be specific.
> "noapic" does not and never has had anything to do with the
> local APIC, only the I/O APIC. There is currently no kernel
> option for preventing the local APIC from being enabled if
> the kernel was built with local APIC support.

 Well, "nosmp" does exactly that for a SMP-capable kernel -- it could be
trivially reused for a UP-APIC configuration (the case is obscure enough
not to invent another option). 

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +

Re: turning off APIC

[Andriy Rysin]

>
> On Sun, 15 Sep 2002 14:28:44 +0300, Andriy Rysin wrote:
> >If APIC is compiled in the kernel (wich is the case with most
> >distributions) when I start kernel with "noapic" option, APIC is getting
> >enabled anyway and only later gets disabled. This causes problems on
> >some VAIO notebooks - it seems like BIOS gets confused if APIC was
> >turned on (particularly on my laptop when I try to reboot from Linux it
> >hangs saying that thera problems with keyboard). That would be much
> >better to have an option to turn it off in the boot options and not to
> >recompile the kernel. Could somebody comment this please?
> >Please CC me on this email address.
>
> Which APIC? local or I/O? Please be specific.
> "noapic" does not and never has had anything to do with the
> local APIC, only the I/O APIC. There is currently no kernel
> option for preventing the local APIC from being enabled if
> the kernel was built with local APIC support.
>
> You have four options:
> 1. Recompile with CONFIG_SMP=n and CONFIG_X86_LOCAL_APIC=n.
> 2. Run dmidecode on your Vaio, dig out the identification strings,
>    and add them to arch/i386/kernel/dmi_scan.c's local APIC
>    blacklist.
> 3. Add a __setup in arch/i386/kernel/apic.c after the declaration
>    for dont_enable_local_apic, which sets it to 1.
> 4. Tell Sony to fix the Vaio's BIOS.
>
> /Mikael


Thanks Mikael, item 2) seems to be most reasonable. I did not know there 
are different APICs, though what's interesting is the line in 
kernel-parameters.txt
 
    noapic        [SMP,APIC] Tells the kernel not to make use of any
            APIC that may be present on the system.

Note: not to make use of _ANY_ APIC that may be present......
I would suggest either "noapic" should turn off ALL APICs as is 
described in the doc or fix the doc. Personally I like fist option 
better though second is much simplier.

Andriy

turning off APIC

[Andriy Rysin]

If APIC is compiled in the kernel (wich is the case with most 
distributions) when I start kernel with "noapic" option, APIC is getting 
enabled anyway and only later gets disabled. This causes problems on 
some VAIO notebooks - it seems like BIOS gets confused if APIC was 
turned on (particularly on my laptop when I try to reboot from Linux it 
hangs saying that thera problems with keyboard). That would be much 
better to have an option to turn it off in the boot options and not to 
recompile the kernel. Could somebody comment this please?
Please CC me on this email address.

TIA,
Andriy