[mythtv-users] PII 450 system

[Brian Foddy]

On Tuesday 10 June 2003 03:50 pm, Allen T. Gilliland IV wrote:
> Is mythtv even capable of taking advantage of dual
> processor systems?  You obviously need kernel smp
> support, but doesn't the application also have to have
> its own smp support?
>
> Yeah ... a pII 450 with a PVR-250 ought to work fine
> for recording, but you won't do very well with
> playback since decoding takes a number of cycles as
> well.  I do recordings in mpeg4 at 640x480 with high
> settings and I haven't been able to get my xbox to
> play back smoothly yet.  So thats a pIII 733.
>

Allen,

Its really not too bad, but could always be better.
Mythtv has several threads per recording and a
couple per playback.  So even recording a single
stream, there will be some advantage to a SMP box,
ie: the video compression, audio compression,
reading from the capture card, writing to the disk
I think are all different threads (one of the 
primary developers may correct me on this).  But
then add a second or third capture card and now
you can realistically get 2 CPUs each compressing
a video stream at the same time (the hardest job).

What it can't do, is use 2 cpus to compress 1
video stream (other than the supporting threads
I mentioned). 

And dont forget all the system overhead
of the file io, raid control, video buffers, etc.

The end result on my dual P2-450 is while the absolute best
resolution I "could" use is a single 480x480 if I 
was lucky, I find it can do 2 640x240 recordings
and a playback, or 3 640x240 (1 is a pvr) without
a playback.  This is of course using my quality
settings...
rtjpeg @ 200, no sound encoding, no deinterlacing
but if I just want to watch an average TV show
say the news or other simple stuff, its fine for
me.  I don't try to watch fast moving sporting 
events with these settings, and when I want to
watch an HDTV show like CSI, well there is no
comparison.  But its all what your expectations
are.

As for me, this box was a left over from a system
upgrade I did about a year ago and only have
a couple hundred $$ plus capture cards in it.
Eventually I'll put some extra $$ together and
do a serious upgrade to either a very fast single
cpu machine or another faster dual, but from my
estimates that would still run over $1000 and
I really just can't justify that money just to
get a better picture quality right now.

As for the PVR250, the best I've been able
to decode is 592x480 with the box doing nothing
else.  Clearly 450Mhz is right on the low
side for a single, but its usable.

So yes, myth will use a SMP box, if the job
is right, but you can't simply multiply the
MHz by 2 and expect twice the performance.

Brian