[mythtv-users] Re: HDTV, Myth, HD-2000, HD-3000, questions galore (and hopefully answers from the smart people... )

[Brad Templeton]

On Sat, Jan 29, 2005 at 02:02:57PM -0500, James Armstrong wrote:
> Brad Templeton wrote:
> 
> I am getting the following while watching HD 1080i on CBS:     38% User, 
> 2.2% System and 56.1% Idle
> 
>    .3% cpu usage for mythfrontend
>        mythbackend on another computer
>    12% for X
>    .3% for lirc_dev
>    <1% for top and others
> 
> This is on a 3gig Pentium4 HT with 8meg cache. 1gig memory, NVidia 5200.

Yes, as noted, the HT P4s reprot very good numbers, though there's been
some recent debate off list about whether they are true or not, I'm
still researching it.

Hyperthreading, for those who don't know, means the P4 pretends to
be a dual-processor system by duplicating the registers and various
elements of the ALU, but not the entire CPU by any stretch. 

This means that for certain algorithms, ones that are ALU bound rather
than memory bound, and which are multi-threaded, you can see a real
improvement.   There is speculation that mpeg encode and decode are
in this category.  But it makes it hard to figure out how "idle" the
processor is because sometimes one of the units may be "idle" but in
fact it could not really do anything.

So we need to do some tests as follows:
    a) Try mpeg decode on a P4 with the non-SMP kernel.
    b) Get a benchmark program which can be run niced, to try to 
       figure out how much spare capacity each different test system
       has while playing 1080i.

Note that this just tells us how much spare capacity there is to run
the benchmark program.

What we care about is the following though:
    
    a) Is there enough spare capacity so that when minor system tasks
       take place, they don't make video skip.

    b) Is there enough capacity to do that if you also throw in a niced
       thread to do commercial elimination or transcode?

    c) Do we have enough capacity to handle "peak" decoding load, since
       that varies with scene complexity.

And also

    d) What's the cheapest processor we can get away with and still play
       skip-free 1080i and 720p?


xvmc of course can also change this equation a lot.   On my P4, for example,
playing 1080i in mplayer with xvmc, I have seen idle times over 80% which
sounds good and implies one could get away with something much less in
this environment.