[mythtv-users] Reducing system resources (cpu, memory)

[Ray Olszewski]

At 08:40 AM 2/25/2004 -0800, Donald McLennan wrote:
>Hi,
>I have MythTV running on a 450Mhz computer with
>PVR-250. Like other users with similar low end
>configuration, Mythtv works, but is slow.
>
>Are there any suggestions on minimizing the cpu and
>memory requirements by disabling various linux
>services to get any better performance? What are the
>minimal linux services that need to be running?
>
>Are there any key MythTV settings like picture size,
>resolution, etc., that would improve performance?
>
>Would a PVR-350 card make any difference?
>
>Or, as others have commented, do I need a faster cpu?

If you had a bttv card ... one that uses software encoding ... there would 
be a lot you can do to fiddle with resource use. But if you had such a 
card, decent performance would be so far out of range on a 450 MHz CPU that 
it wouldn't be worth trying.

With what you do have ... the problem is that the PVR250 handles the 
encoding load, but it leaves decoding to software ... and MPEG2 decoding is 
more demanding of CPU than other codec choices, such as MPEG4.

The one thing you can try is reducing the capture resolution. Go down to 
320x240 (for NTSC; the corresponding PAL values are a bit different). That 
will lighten CPU load considerably, perhaps even enough to make it work ... 
but only you can decide if the resulting picture quality is "good enough".

As to the minimal Linux services ... all you really must have working is 
the kernel itself, configured to support networking; logging (syslogd and 
klogd); and crond (for things like getting program data updates). The SQL 
database doesn't need to be on the same machine, but if it is, then mysql 
too. Depending on how you access the machine and its filesystems, you may 
need to run various other daemons (sshd, httpd, smbd, nfsd) ... all that 
varies by site. Of course you need X running. Except for X, it would be 
unusual for any of this stuff to be putting much of a load even on a 
low-end CPU.

Of course, the usual odds and ends apply to your situation (probably; 
"slow" isn'y a very complete problem description, so I'm guessing about how 
the actual problem presents itself). Make sure X is using xVideo to display 
video. Make sure DMA is enabled on the hard drive. You don't say how much 
RAM you have ... recommandations vary, but I think the consensus is that 
256 MB is the recommended minimum, and 128 MB the bare minimum ... mostly, 
this will get used to buffer video. Make sure your source signal is fairly 
clrzan ... codecs see most video interference as information to be encoded, 
so struggle more with bad signals than with good signals (my hardware-based 
encoder drops a lot of incomiong frames when the signal is bad).

A PVR350 does decoding in hardware ... to its TV-out, at least ... so 
should "make a difference". I don't use one myself so I cannot say if it is 
*enough* of a difference or not ... though I'd *guess* it is enough.

Personally, I think you need a faster computer, when all is said and done.