[mythtv-users] Will moving to DDR-400 memory from DDR-333 improve performance?

[Paul Catchpole]

For what it's worth...

The RES column is (according to the docs for 'Top') the most appropriate
descriptor for actual memory usage: 

16735  8.4  600m 568m  31m  944 562m 7344 1631    0 S  15   0  0.7
mythbackend

10158  3.2  145m 133m  12m 5712 135m 2284 2695    0 S  16   0  0.0 mysqld

So on the backend (2x DVB-T, 384mb RAM, P4 2.4ghz), mythbackend is using
31mbytes of RAM and mysql is using another 12mbyte. 

On the diskless frontend, served off the above backend: 

5067 49.8  250m 126m 124m 1312 173m  41m  229    0 S  15   0 50.8
mythfrontend
  7456 32.7  237m 156m  81m 1312 164m 1492    0    0 S  15   0  0.0
mythfrontend
  5057 18.9  114m  67m  46m 1532  25m  21m   35    0 S  15   0  10.5 X

So I've two (not quite sure why...) frontend processes, using 124 and
81mbyte, with X using 46mbyte. 

Just for interests' sake... 

Paul 


---
Paul Catchpole CCNA
Consultant Network Specialist
 
-----Original Message-----
From: mythtv-users-bounces at mythtv.org
[mailto:mythtv-users-bounces at mythtv.org] On Behalf Of Joe Votour
Sent: 23 October 2006 16:16
To: Discussion about mythtv
Subject: Re: [mythtv-users] Will moving to DDR-400 memory from DDR-333
improve performance?

> On Sun, 2006-22-10 at 23:37 -0700, Yeechang Lee wrote:
>> I currently have 1.5GB of DDR-333 memory
>
> Does it not strike anyone else that this kind of memory requirement for
> a STB is absolutely ridiculous?
>
> OK, 1.5GB is probably overkill, but the 256MB I have in my FE/BE has, as
> of 0.20, become far too small to be able to run a full myth system in.
> Even with a 1G of swap, during a mythfilldatabase the machine thrashes
> the swap and frequently the OOM killer is invoked and ends up killing
> mysqld.
>
> Why is Myth using so much memory as of 0.20?
>
>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>  6846 root       0   0  165m  39m  11m S  0.0 15.9 365:30.06 mythfrontend
>  8153 root       0   0  206m  15m   9m S  0.0  6.4  11:44.56 mythbackend
>
> Like seriously... 206MB for the backend and 165M for the frontend?
>
> Is this just my system or are most peoples 0.20 systems showing the same
> kind of memory use?
>

It is unfortunately the bloat of Linux and X11/Qt sneaking up on us. 
Believe me when I say that unfortunately, I could not do a better job
(except maybe use something other than Qt, but that's just because I'm a
poor C++ programmer).

If you want to trim down the memory, then you basically need to make the
machine a dedicated MythTV machine, with a stripped down kernel for only
your hardware and maybe even compile MythTV against uClibc.  You'd also
want to selectively compile options out of MythTV as well.

Most Linux-based set-top boxes use a CPU in the range of 200MHz and 32 or
64MB of memory.  Of course, they also don't use X (they use MicroWindows
or something smaller than X), they have dedicated MPEG-2/MPEG-4 decoding
chips (thus no need for software codecs), and their kernel is stripped
down to less than 1MB, they use BusyBox, etc., etc.

Also, most people are running both the frontend and the backend on the
same machine (although I am not).  This has higher memory requirements
than just a regular set-top box.  In terms of the servers that the cable
operators use, they are massive, and the set-top boxes, as I described
above, are puny - unless they run that bloated OCAP or OpenTV crap.

All in all, the memory usage isn't too bad for a Linux machine doing this
stuff.

-- Joe


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