Hardware for pvr

[Lennart Sorensen]

On Sat, Mar 12, 2005 at 05:37:04PM -0500, D. Hugh Redelmeier wrote:
> | From: Amos H. Weatherill <right_maple_nut-/E1597aS9LT10XsdtD+oqA at public.gmane.org>
> 
> | Also, I wound recommend an AMD processor for this kind of task because
> | the extremely deep pipelines on the Pentium 4 processor can impact
> | the computers ability to multitask effectively in this situation.
> 
> Are you making that up, or is that based on measurement?

In what I have seen, the P4 wins on code optimized for long runs of SSEx
execution (where a few instructions can really use the resources and
memory throughput of the P4), while code that is less linear and has
lots of conditions runs much better on the Athlons and the Pentium M.
This does make sense since a high clock rate long pipeline cpu would run
fast on linear code, and not well on branch heavy code.

> My intuition is that the pipeline is something like 30 cycles long.
> This is 10 nanoseconds at the 3.0GHz he is contemplating.  Say there
> are several instructions in flight that need to be completed, so let's
> multiply by 10 -- 100ns.  The other things going on in a task switch
> dwarf a 100ns penalty.

It still hurts on branch mispredictions.  Unless your software takes
advantage of the P4's rather good SSE2/SSE3 instructions, it will loose
to an Athlon (especially an Athlon64 which too is rather good at
SSE2/3).

> My impression is that doing the compression in the video card is much
> wiser.  Hauppauge PVR 250s go for $150 on sale; sometimes even less.
> Then you can use a CPU as slow as a Pentium III, I think.
> 
> There are newer models from Hauppauge.  They may be cheaper.  They may
> be supported.  Other companies also produce compressing tuners.

Certainly hardware is nice, but only MPEG2 is cheap to buy in hardware.
I haven't personally seen an MPEG4 hardware encoder, although it is
certainly possible they exist.

> More than is needed, I think.  Depends on your goals.  Don't forget
> "quiet" -- a noisy audio-video appliance is annoying.

Even a noisy PC is annoying. :)

> | $324.99   Intel? Pentium? 4 -630, 3.0-GHz @ 800Mhz w/ 2Mb
> |           EM64T XD (Socket 775)  w/ Heat Sink & Fan
> 
> Sounds sexy.  Not necessarily usefully so.

The EM64T stuff certainly doesn't do much useful on a typical desktop
machine with 1 or 2GB ram.

> I am trying to bring up a PVR 250 on an x86_64 system.  Not all of the
> software seem to be ready for x86_64.  Soon, I hope.

There certainly seems to be a lot of work going on with it and a lot of
interest in it.

> Why am I using x86_64?  Not for video reasons -- this is to be my
> general purpose desktop machine.  x86_64 is a good source of low-grade
> challenges.

And faster and cheaper than similar P4s.  Working out 32 to 64bit
problems is lots of fun I imagine.

Lennart Sorensen
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