Message-ID: <45C35024.8090907@tmr.com>
Date: Fri, 02 Feb 2007 09:52:20 -0500
From: Bill Davidsen <davidsen@tmr.com>
Organization: TMR Associates Inc, Schenectady NY
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To: Lapo TIN <lapolapolapo@tin.it>
CC: linux-smp@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: smp and irq conflict
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Lapo TIN wrote:
> Dear all,
> I have a problem with IRQs.
>
> My pc has a CPU PentiumD945 (dual core) and a 2.6.19smp kernel.
> I have two video acquisition board (four bt8t8 each) in the only two pci
> slots of my motherboard. Thus I have a total of 8 bttv modules that are
> working together, and the /proc/interrupts is as follows:
> # cat /proc/interrupts
>            CPU0       CPU1
>   0:      13575          0   IO-APIC-edge      timer
>   1:          2          0   IO-APIC-edge      i8042
>   4:         11          0   IO-APIC-edge      serial
>   8:          1          0   IO-APIC-edge      rtc
>   9:          0          0   IO-APIC-fasteoi   acpi
>  12:          4          0   IO-APIC-edge      i8042
>  14:      22286          0   IO-APIC-edge      ide0
>  17:       7073       2097   IO-APIC-fasteoi   uhci_hcd:usb5, eth0
>  18:       2525          0   IO-APIC-fasteoi   bttv0, bttv7
>  19:       2829          0   IO-APIC-fasteoi   bttv1, bttv4
>  20:       2526          0   IO-APIC-fasteoi   bttv2, bttv5
>  21:       2226          0   IO-APIC-fasteoi   bttv3, bttv6
>  22:          2          0   IO-APIC-fasteoi   ehci_hcd:usb1, uhci_hcd:usb4
>  23:         86          0   IO-APIC-fasteoi   uhci_hcd:usb2
>  24:          0          0   IO-APIC-fasteoi   uhci_hcd:usb3
> NMI:          0          0
> LOC:      13484      13502
> ERR:          0
> MIS:          0
> You can see that IRQ18 is shared between bttv0 and bttv7, IRQ19 between
> bttv1 and bttv4 and so on.
>
> Sometimes it crashes. It seems a matter of conflict in IRQ.
> With only one video board everything is ok, but with two, they shared irq
> and something goes wrong... 
> How can I tell to the kernel to not to share the IRQ for these boards ?
> I think (I don't know if I'm right) that this could be the problem.
>
> I even tried with another motherboard, and doing cat /proc/interrupts the
> situation was the same, except for 'eth0' that was together with bttv0 and
> bttv7... so it was even worst ! it crashes after few minutes.
>
> I tried to read IO-APIC.txt in Documentation/i386/ folder, but I didn't
> understand how to avoid the coupling of IRQ.

You may be able to move one board to another slot, but looking at the 
bandwidth I suspect you may need a server motherboard with multiple 
busses, preferably running at 66MHz 64bit. I don't think this is a 
interrupt problem, but you can just try capture on two channels which 
share an interrupt, like bttv0 and bttv7 to verify that.

I think you are just running out of bus.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

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