linux-kernel - Re: PATCH: (v2) Allow over-ride of smp_found

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Message-ID: <498C90D5.9030400@kernel.org>
Date:	Fri, 06 Feb 2009 11:34:45 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Randy Dunlap <randy.dunlap@...cle.com>
CC:	Ben Greear <greearb@...delatech.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	linux-kernel <linux-kernel@...r.kernel.org>, len.brown@...el.com
Subject: Re: PATCH:  (v2) Allow over-ride of smp_found_cfg with kernel cmd-line
 option.

Randy Dunlap wrote:
> Ben Greear wrote:
>> Ingo Molnar wrote:
>>> * Ben Greear <greearb@...delatech.com> wrote:
>>>
>>>> Allow user to keep smp_found_cfg set to 1 even if MADT
>>>> cannot be parsed.  This works around funky BIOS on FWA-7304
>>>> (VIA CN700 chipset) system, and possibly other systems as well.
>>>> Without this override, performance drops by around 15% on
>>>> network throughput tests on this system.
>>> I'd _much_ rather have a warning message printed and have a default,
>>> unconditional fallback to mptable parsing in this case.
>>>
>>> I.e. same end result just no ugly and inconvenient force_smp_found_cfg.
>>>
>>> The mptable works fine in most such cases to enumerate apic details.
>>> (as it does in your case, evidently)
>>>
>>> And if both the ACPI and the MPTABLE is hosed on a box, it cannot be
>>> of much use on other OSs either, right?
>>>
>>> So please do a patch that removes the 'smp_found_config' and which
>>> changes the warning message to warn about no ACPI table in the MADT
>>> table. Ok?
>> An updated patch is attached.  It's also inline below, but I'm sure the
>> inline version is white-space corrupted.
>>
>> Do not disable mptable parsing just because there is no ACPI table
>> in the MADT table.  This effectively backs out changeset
>> 7b37b5fd9ba32c0c5afc3537eed7e7466f2173e2
>>
>> Signed-Off-By:  Ben Greear<greearb@...delatech.com>
>>
>> Thanks,
>> Ben
>>
>>
>> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
>> index d37593c..74a50b6 100644
>> --- a/arch/x86/kernel/acpi/boot.c
>> +++ b/arch/x86/kernel/acpi/boot.c
>> @@ -1379,12 +1379,14 @@ static void __init acpi_process_madt(void)
>>            * ACPI found no MADT, and so ACPI wants UP PIC mode.
>>            * In the event an MPS table was found, forget it.
>>            * Boot with "acpi=off" to use MPS on such a system.
>> +         *
>> +         * NOTE:  This assumption seems wrong in at least some cases,
>> perhaps
>> +         *  when ACPI is off in the BIOS.  Changing to a warning without
>> +         *  setting smp_found_config to zero.
>>            */
>> -        if (smp_found_config) {
>> +        if (smp_found_config)
>>              printk(KERN_WARNING PREFIX
>> -                "No APIC-table, disabling MPS\n");
>> -            smp_found_config = 0;
>> -        }
>> +                "WARNING: No ACPI-table found in the MADT\n");
> 
> 		                APIC table
> 

APIC-table == MADT

could just use

WARNING: No APIC-table found

YH
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