[mythtv-users] Re: Draft revisions to HowTo section 3.3, second try

Ray Olszewski ray at comarre.com
Thu Apr 24 11:05:48 EDT 2003


Your comments here make me glad I wrote the original statement you are 
responding to. There are too many details like this that we do not discuss, 
perhaps because we all think the answer is obvious. But we arrive ay many 
different "obvious" answers. There's an old saying -- "Things that go 
without saying ... usually go better when said" -- that may apply here.

That said, I have a couple of questions about your report.

1. You say faster memory "had a dramatic effect on MythTV performance". In 
what way? What was better about the PC133 systems?

2. You say that for either type of memory you tested, your test system 
"performed nearly identically with a PIII-700 and Celeron-1.4 on MythTV". 
Again, measured by what standard? My experience is that P-III and Celeron 
chips are almost identical in their performance when doing video capture, 
but that means that clock speed is everything in these comparisons. So I'd 
expect your test to show the (slow) P-III running at almost twice the CPU 
load as the (fast) Celeron.

3. Based on a comparison of PC100 and PC133 RAM, you conclude that "if you 
can, use DDR memory systems". This seems to be extrapolating your 
observations outside their range (PC100 versus PC133). Do you have any 
additional reason for favoring DDR memory over PC133? Given its 
considerably higher cost, the move isn't trivial, whereas these days it is 
all but impossiable even to find PC100 memory (to be honest, when I wrote 
what I did, I was not thinking of PC100 as a "ommon type of RAM in use 
today" ... though you can hardly be criticized based on my imprecision).

At 08:47 AM 4/24/2003 -0400, you wrote:
> > 3.3.2 Memory
> >
> > A MythTV host that is both a backend and a frontend, and that uses
> > software encoding with a single capture card, should run comfortably in
> > 256 MB of RAM; depending on other hardware choices, even less (128 MB)
> > might suffice. Any common type of RAM in use today is fast enough.
> > Additional RAM is useful, but it mainly serves as buffer space to smooth
> > the process of sync'ing to the hard disk. For that reason, a swap
> > partition is effectively useless.
>
>My experience relates directly to this issue.  I have experimented with two
>different motherboards (Via VA6 and Shuttle FV25) two different processors
>(PIII 700 MHz and Celeron 1.4 GHz), two different sets of memory SIMMs
>(PC100 and PC133), and various clock speeds.  While processor speed is
>certainly a factor, the primary factor in MythTV performance is memory
>access speed.  By "MythTV performance" I mean the maximum resolution and
>quality readily achievable with a given codec for recording only.
>
>For example, the same motherboard (VA6) with the same memory SIMMs (PC100
>and also PC133) performed nearly identically with a PIII-700 and
>Celeron-1.4 on MythTV.
>
>The same processor (Celeron-1.4) on the same motherboard (VA6 and also
>FV25) with different SIMMs (PC100 vs PC133, with memory clock speed
>adjusted accordingly) had a dramatic effect on MythTV performance.
>
>In overclocking mode, tweaking the processor clock speed did not have
>nearly the effect that tweaking the memory clock speed did.
>
>This all makes sense: video applications typically have high miss rates at
>the cache and are thus memory bound.
>
>The conclusion: faster memory systems will work better.  If you can, avoid
>PC100 memory and systems.  Similarily, if you can, use DDR memory systems.
>
>Does anyone have a set up with other motherboards (eg, Via EPIA) who can
>perform similar tests between memory speeds?  Or a motherboard which
>supports PC133 as well as DDR?







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