Re: Regression on VIA C3 motherboard, commit: 66f2173e2

[Ben Greear <greearb@candelatech.com>]

Robert Hancock wrote:
> Ben Greear wrote:
>> I have a via motherboard with C3 processor and some real-tek NICs.  I 
>> noticed
>> when using the top-of-tree that performance on it sucked (30Mbps v/s 
>> 54Mbps
>> network throughput in one pertinent test).
>>
>> After several hours of bisecting, I see this as the culprit:
>>
>> 7b37b5fd9ba32c0c5afc3537eed7e7466f2173e2 is first bad commit
>> commit 7b37b5fd9ba32c0c5afc3537eed7e7466f2173e2
>> Author: Len Brown <len.brown@intel.com>
>> Date:   Tue Dec 23 01:47:42 2008 -0500
>>
>>    ACPI: disable MPS when NO APIC-table found
>>      When ACPI is asked to find an MADT (APIC table)
>>    and fails, then ACPI expects to run in PIC mode.
>>      However, if an MP Table is was found, IRQs will be
>>    registered as if an IOAPIC is being used, even
>>    though ACPI is configuring interrupt links links for PIC mode.
>>      In this scenario, disable MPS so that IRQs
>>    are registered in PIC mode, consistent with ACPI.
>>      http://bugzilla.kernel.org/show_bug.cgi?id=12257
>>      Signed-off-by: Len Brown <len.brown@intel.com>
>>
>> :040000 040000 86ce74daee3a9fe6ff21ef7f8fb364af23ec0c1e 
>> 364933dfec0df34e63b1aeff6aff4092d421886b M      arch
>>
>>
>> In addition, I see this warning in my logs, which is likely the symptom:
>>
>> ACPI Exception (tbxface-0627): AE_NO_ACPI_TABLES, While loading 
>> namespace from ACPI tables ]
>> ACPI: Unable to load the System Description Tables
>
> You're getting this on boot:
>
> ACPI Error (tbxfroot-0218): A valid RSDP was not found [20080926]
>
> That essentially means ACPI isn't working at all, I think. Did 
> previous kernels produce this error? Do you have ACPI disabled in the 
> BIOS or something?
>
Er, yes...I have ACPI disabled in the BIOS.  I seem to recall now that 
it worked around
some instability, but it's been a few years since we set that up.   
Still, it was working
fine before, and fine again when I comment out the change in this commit 
(and another
change to force the 'tsc' to be considered stable).

The same error message happens as far back as 2.6.25 at least.

Thanks,
Ben

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-- 
Ben Greear <greearb@candelatech.com> 
Candela Technologies Inc  http://www.candelatech.com