[linux-dvb] Re: DVB-T crashes Mandrake 9.1

[Bruno Prior <bruno@rpgd.uklinux.net>]

Hi Philip,

Philip Armstrong wrote:
> Linux is perfectly capable of supporting irq sharing. A cursory glance
> at /proc/interrupts on my machine reveals that the interrupt for my
> dvb nova-t card is shared with both my ethernet card and my wireless
> ethernet card for a start.
So this would seem to indicate that the IRQ-sharing culprit is not the DVB 
driver, otherwise you would be having problems. Is that a fair conclusion? 
If so, it suggests the culprit must be the driver for eth0, the other item 
sharing this interrupt. This is an onboard Gigabit ethernet port, using the 
e1000 driver.

On the other hand, if you look in the archives for a message from me on the 
"dvbtune / Nova-T unable to lock on frequency problems" thread dated 
15/04/03, you will see that the Nova-T was sharing interrupt 21 with eth0 
when I was playing with this previously, and I never experienced irq loops 
and eventually got it working. So maybe this is a red herring.

> However, it may be that for some reason your hardware isn't being
> setup correctly in this case, or it may be a driver bug which shows up
> only with shared interrupts -- failing to clear an irq after you've
> handled it for instance works ok unless you're sharing the interrupt
> in which case it'll cause lockups on the spot (iirc). Any of the
> drivers which handle the hardware on the shared interrupt could be
> responsible for this problem.
As above, the same drivers were sharing the same irq previously, and not 
having problems, so I guess it isn't this.

> Also, you don't actually say which motherboard you have, but it seems
> to have an awful lot of unrecognised hardware; I'd have a look on the
> linux-kernel mailing list to see if there are any reports of problems
> there. 
It's a Gigabyte GA-8PE667 Ultra2. I don't see any unrecognised hardware - 
only unknown subsystems for the onboard gear. On the face of it, it seems 
like an excellent board, and was running very happily until the DVB 
problems. It's based on the Intel 845PE chipset, with 1 AGP and 6 PCI slots. 
It has support for 4 IDE channels (2 on the Intel chipset, 2 on a Promise 
PDC20276 controller, that also provides RAID support, which I am not using), 
and 2 SATA ports, also with RAID support. It has onboard Gigabit ethernet, 
using the Intel Kenai-32 chipset. You can get most of the rest of the 
features from the output of lspci in my previous message - basically this 
board seems to have everything but the kitchen sink. But as I have mentioned 
previously, this board was running fine until I tried DVB the other day, so 
I don't think it is anything intrinsically wrong with the board.

> Oh, and Mandrake 9.1 is using some hacked up prerelease of the
> 2.4.21 kernel. I doubt it's been well tested on the kind of server
> hardware you're using -- Mandrake are not known for their server-side
> support afaik -- they seem to concentrate mostly on the end-user
> gui experience.
I would say that's harsh. Agreed, Mandrake do not focus on the Enterprise 
market like RedHat and SuSE, but they are not as desktop-focussed as (say) 
Lindows, Xandros or Lycoris. One of the reasons I like Mandrake is that they 
have historically found a happier middle line (IMHO) than other distros in 
support for server and desktop features. If they were desktop-focussed, 
would they be producing Enterprise kernels, firewalling versions of their 
distro (the MNF) and developing features such as drakTermServ, a very 
promising system to setup a Mandrake server to provide Terminal Server 
facilities to Mandrake clients?

You may be right about the 2.4.21 pre-release kernel, but my understanding 
is that the Mandrake-patched kernel versions were intended to be equivalent 
to (though undoubtedly inferior in practice) an -ac-patched kernel. And in 
my experience, you are better with an -ac-patched kernel, either pre- or 
post-release, than with the vanilla version. There may be problems with the 
Mandrake 9.1 kernel, but it's the same kernel version I was using when I got 
DVB working previously (see the message to this list of 15/04 quoted 
previously). This is a fresh install of Mandrake 9.1, and also a 
newly-compiled kernel, but it was working on the previous Mandrake 9.1 
install, so the problem does not lie intrinsically with the Mandrake-patched 
kernel source. It might, on the other hand, lie with my choice of options to 
compile into the kernel (I have to use a recompiled kernel to get the 
PDC20276 to work).

> One thing which did spring to mind after looking at your logs was that
> you could try booting with noapic to turn off apic support; if it's
> the interrupt routing which is being mishandled then turning off the
> apic support might help.
This is an excellent idea. I always used to add this to my bootparams (it 
seems, along with acpi=off and ide=nodma in extremis, to solve a whole host 
of Mandrake problems), but I have been trying without on the server, to see 
if it was still required. Until now, I didn't seem to need it - everything 
was working fine. I have no idea what the APIC does, but if you say it is 
related to IRQ issues, then this sounds like a good bet. I'll give it a go 
(and cross my fingers, because everytime I have to hard reset this machine, 
I have to resync 360Gb of RAID arrays, which is pretty tedious).

Thanks for your help. It was very informative.

Cheers,

Bruno Prior



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