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

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Date:	Fri, 06 Feb 2009 11:30:48 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Ben Greear <greearb@...delatech.com>
CC:	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	"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.

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

>      }
> 
>      /*
> 
> 
> 


-- 
~Randy
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