[mythtv-users] Dual Tuner CPU Scaling

[Shawn Asmussen]

Well, it's kind of hard to say without more information. The info in those
graphs isn't very helpful for tracking down this kind of problem.
Processes don't always scale completely linearly in these kinds of
situations. One reason is context switching, which is the overhead
involved in switching back and forth between processes. That's probably
not enough to cause the size of difference you're seeing though. As one
person already mentioned, if you're running low on RAM when you're
encoding two shows at once, a big performance hit could result. If you
were to post some more info, we might be able to help you determine where
you're problem lies. If you were to capture the output of this command:

top -b -n 1 | head -25

both while one show is recording, and while two shows are recording, so
that we can see the difference, that would probably be a good starting
place. Top is often a good starting point in these kinds of situations,
and the -b option will tell it to run in batch mode, with the -n 1 option
telling to to just run once and exit instead of running every 5 seconds
which is the default. That should give us an idea of what processes are
using how much cpu time, and what your memory utilization looks like.

Shawn Asmussen

Kyle E Wenda said:
> I have noticed that when performing one recording, my P4/1.8 dual-bttv
> machine will run at about 35% CPU load with MPEG4 encoding.  When
> performing two recordings, you would expect the load to be 70% or so,
> but it is not - it is pegged at about 98%.  A couple of frames from each
> recording are dropped per minute, but it's hardly noticeable.  My
> question is, why doesn't this scale like you would expect it to?  I was
> thinking I might be able to jam 3 cards into the machine, if the
> recordings scaled properly.
>
> See system stats here:
> http://dsl.kylewenda.com/stats/mrtg/blaster-stats.html  Blue line
> represents CPU load as a percentage, and fill color represents amount of
> free video storage space as a percentage.
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Shawn Asmussen