[mythtv-users] Suggestions for a stable backend

[Mike Thomas]

On Thu, 30 Jan 2014 18:42:17 -0800
EJS <ejshoor at yahoo.com> wrote:
> Hi there,
> 
> My backend works but it just isn't very stable.  It experiences two
> types of crashes relatively frequently (one every other day or so).
>  The first one is  a kernel dump that typically occurs when both of
> my tuners are recording at the same time- although not always.  The
> second type occurs when the whole box just freezes and won't respond
> to any keyboard/mouse input.  This one doesn't seem to be related to
> recording.
> 
> I had taken the kernel dump problem as far as I could.  It seems to
> have been introduced on 12.04, but i haven't seen any resolutions.
>  The second problem doesn't write anything to the log files so I am
> not sure how to even begin to debug.  

Dear J,

This kind of thing can be hard to diagnose, so try this approach:

First turn off mythbackend and mysql so they don't get damaged. Then
try parallel-building (make -j 4 or more) something big, like the
kernel, openoffice or firefox with static libraries. Do this over and
over again. If you have a memory problem it will show up after a few
days as a spurious compiler error. memtest's pattern testing is less
likely to report problems. This will help you to establish whether the
platform as a whole is stable.

If you are seeing problems with that, you most likely have a hardware
problem, so try this:

Enter your BIOS settings screens and turn off /all/ those speed-up
tweaks you set. Set everything to 'Auto' or 'Standard' or 'Normal'.
Over-clocking RAM, CPU and especially PCI busses are bound to cause
problems. I've experienced bad memory timing causing USB modem line
drops (but no other problems). Unless you've cooked your parts, I'd
expect any problems due to over-clocking to go away.

Disconnect your tuners. If you can, plug in an old PS/2 keyboard (or
use an adapter) and plug in an old (non-accelerated) PCI or PCI/Express
video card that you know works and set the BIOS to use that card as the
primary video adapter (this is automatic on most BIOSes). Boot your
kernel with vga=normal or some other parameter which stops your kernel
from entering graphics mode. Clearly you'll need to work in single user
mode, over a serial console or via ssh as xdm won't work. Repeat the
compilation tests. If you still have problems you can start swapping
parts.

If you don't think it's hardware, it's probably drivers. I had
problems with one of my computers because the kernel's video drivers
couldn't support 2 video cards run by different X servers. It
introduced all sorts of instability including causing the machine check
routines to spew out HARDWARE ERROR. The nature of the 'HARDWARE ERROR'
changed as the kernel changed. Anyway, the point I'm making is
something in your software is probably accumulating mistakes until
finally it falls over in a heap, be it with a freeze or a dump.

Try running with a stock kernel. Video drivers and tuner drivers have
changed since 3.2.0 so it might be worthwhile playing with something
more recent. The nub of my message is this: break the problem down to
something very simple and add parts or software step by step.

> 
> In any case, I'd love some suggestions or recommendations for a rock
> solid system.  Here is my current configuration:
> Motherboard:GA-73PVM-S2H/GA-73PVM-S2H CPU: Intel Core 2 Duo E8600
> Wolfdale 3.33Ghz Ram: 2GB
> Tuners: 2  HVR-1250
> Mythbuntu 12.04
> Linux version 3.2.0-33-generic
> 

I use this:

Dual Celeron 2.5GHz, 4GB 800MHz RAM, 2 x 7200rpm 1.5TB HDDs, 2 x RV710
graphics cards, 3 x HVR2200 tuners.

I am able to record digital broadcasts on 6 channels, play different
recordings on both graphics cards and play recordings on two other
computers simultaneously without any problems. This was also the case
when I used a dual 2.2GHz Celeron with 2GB RAM. I don't receive any HD
transmissions.

> mythbackend version: fixes/0.26 [v0.26.0-42-g10479af]
> 
> The backend also runs a SD front end that I use on occasion, but it
> mainly drives 2 zotac zbox HD frontends. I record perhaps 5-7 shows a
> week mostly HD QAM. I assume that this isn't considered very heavy
> usage.

Not to me, HD excepted.

> 
> Does anyone have any suggestions?  Is my hardware appropriate what
> what I am trying to run?

Looks fine to me.

>  Do I need more ram or a faster cpu?

What does top/htop report when you're doing all this? Mine registers
approximately 0 when recording, 100% per CPU when transcoding
(obviously) and 30-50% per CPU during playback on one of the attached
displays. My remote boxes, even my ATOM laptop, barely register anything
during playback.

If you notice spikes in CPU load and these correspond to anomalies in
the recordings consider increasing the record buffer size using
mythtv-setup.

>  It
> took a lot of tweaking to get the 2 HVR-1250s to run. I like them
> because they are cheap but would a different card be more stable?  I
> had to install a special version of the motherboard bios to get the
> server to even recognize the second card without crashing.

That doesn't sound good. I've had excellent service from my HVR-2200
and HVR-2250 tuners, although occasionally I find they fill the logs
with:

tda10048_readreg: readreg error (r et == -5)
saa7164_cmd_send() No free sequences
saa7164_api_i2c_read() error, ret( 1) = 0xc

Others are better placed to recommend alternatives.

> 
> Would upgrading myth

Unlikely

> or the os make any difference?

Yes. Your problem is at a low level. Sure, it's tickled by user-level
programmes, but what you have is a problem with hardware, device
firmware, device drivers or (possibly) the kernel itself. As you'll
never get the firmware corrected the best you can do is make your
platform stable, upgrade the kernel to suit and if the tuners are still
a problem, replace them.

>  I am willing to
> buy new hardware if its needed, but I'd hate buy new components if
> the problem is really in the software.

Quite so.

> 
> I know this is a relatively vague request, but I'd love some
> suggestions or even example configurations of stable systems similar
> to mine.

Good luck.

Yours,

Mike.