linux-kernel - Re: too low MAX_MP

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Date:	Tue, 1 Aug 2006 01:38:26 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Vitezslav Samel <samel@...l.cz>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@....de>
Subject: Re: too low MAX_MP_BUSSES

On Mon, 31 Jul 2006 13:55:45 +0200
Vitezslav Samel <samel@...l.cz> wrote:

> 	Hi!
> 
>   I tried upgrading our server (i386 arch) from 2.6.16 to 2.6.17 but there
> were some odd messages in dmesg:
> 
> 	MP table busid value (32) for bustype ISA is too large, max. supported is 31
> 
> and (repeated 315 times):
> 
> 	unknown bus type 32
> 
> I found out that 50% of the processor time was spent in softirq and the timers
> ran too fast. I didn't look for what else was wrong.
> 
>   Tracked down to this change in 2.6.17-rc2:
> 
> diff -urN linux-2.6.17-rc1/arch/i386/kernel/mpparse.c linux-2.6.17-rc2/arch/i386/kernel/mpparse.c
> +       if (m->mpc_busid >= MAX_MP_BUSSES) {
> +               printk(KERN_WARNING "MP table busid value (%d) for bustype %s "
> +                       " is too large, max. supported is %d\n",
> +                       m->mpc_busid, str, MAX_MP_BUSSES - 1);
> +               return;
> +       }
> 
>  Uping the MAX_MP_BUSSES value in include/asm-i386/mach-default/mach_mpspec.h
> to 64 makes the machine work O.K.
> The system is HP DL380 g4 with 1 Xeon CPU, kernel compiled non-SMP.
> 
>   Here is excerpt from mptable output:
> ---
> Bus:            Bus ID  Type
>                  0       PCI
>                  1       PCI
>                  2       PCI
>                  3       PCI
>                  4       PCI
>                  5       PCI
>                  6       PCI
>                 10       PCI
>                 32       ISA
> ---
> The last item is the offending one.
> 
> Please, can you consider up the default value of MAX_MP_BUSSES?
> 
> P.S.: also tested 2.6.18-rc3, the same - bad - result
> 

mach-default uses 32 and mach-generic uses 260, so I doubt if there's a big
downside to increasing mach-default.  I expect distros ship with
mach-generic, so you're a rare case.

<tries to remember who works on this and fails>

Andi?  Can you see any problems with increasing the mach-default setting?

Thanks.
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