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 Post subject: Mythtv bottleneck
PostPosted: Thu Sep 06, 2007 10:41 pm 
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Joined: Sun Mar 18, 2007 12:38 am
Posts: 15
My mythbox isn't as snappy as I would like. And I'm considering upgrading.

Specifically, changing channels seems to take a while, and it seems to spend a bit of time writing to the HD sometimes.

Current system;
Sempron 754 3200
512Mb DDR 400
128Mb gf4000 AGP
200Gb samsung PATA
Leadtek DTV1000T
Asus K8N

R5E50

I realize this is pretty low spec. Though I would have though it would be sufficient. Is upgrading the ram & cpu etc going to improve channel changing itc? What about the HD? Or is it due to the dvb card?

I would hate to upgrade and get little improvement!

Cheers


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 Post subject:
PostPosted: Thu Sep 06, 2007 11:01 pm 
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Joined: Thu Mar 25, 2004 11:00 am
Posts: 9551
Location: Arlington, MA
See the MythTV FAQ for this oldie but goodie: http://www.mythtv.org/wiki/index.php/Frequently_Asked_Questions#When_using_live_TV.2C_why_is_there_a_delay_between_the_moment_I_change_the_channel_and_the_time_the_channel_actually_changes.3F


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 Post subject:
PostPosted: Thu Sep 06, 2007 11:10 pm 
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Joined: Fri Sep 19, 2003 6:37 pm
Posts: 2659
Location: Whittier, Ca
I'd say we need a better definition of "snappy"...


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 Post subject:
PostPosted: Thu Sep 06, 2007 11:29 pm 
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Joined: Sun Mar 18, 2007 12:38 am
Posts: 15
thanks tjc,

Would a faster HD noticeably speed things up?

What about faster cpu and more ram speed, higher FSB etc?

Some times it sits there for a few seconds with rapid HD activity, could this be due to running out of ram and using swap?


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 Post subject:
PostPosted: Thu Sep 06, 2007 11:33 pm 
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Joined: Thu Mar 25, 2004 11:00 am
Posts: 9551
Location: Arlington, MA
For HDTV 1Gb is better, but for SDTV 512Mb is plenty.

I've got roughly the same class of CPU and RAM and my performance is fine. The disk buffering time delays are exactly that however, timed delays. Faster CPU and RAM more aren't going to reduce them below those fixed timer values.


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 Post subject:
PostPosted: Thu Sep 06, 2007 11:57 pm 
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Joined: Sun Mar 18, 2007 12:38 am
Posts: 15
thanks, thats what I was wondering.

I'm still a little sus that the HD is slowing things down. Simply because I can hear and see how busy it is.

Do you think a faster HD dedicated to /myth partition might help?


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 Post subject:
PostPosted: Fri Sep 07, 2007 1:52 am 
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Joined: Tue Jan 30, 2007 1:27 am
Posts: 299
We have similar systems. Your CPU is the better end of socket 754. A Sempron is an Athlon CPU with smaller cache. I bet an extra 512 RAM will help though. I just replaced my Sempron 2800 with an Athlon 3200. The menus are faster, but watching recordings is basically the same. I have 1gb.

Hard to say what a faster disk will do, because the HD data stream tops out at less than 20mbps.

FWIW when watching recordings I get an occassional "pause", but also I watch everything at 1.15x speed, minimum :-)


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 Post subject:
PostPosted: Fri Sep 07, 2007 8:58 am 
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Joined: Thu Sep 30, 2004 11:29 am
Posts: 2419
Location: Mechanicsburg, PA
cecil wrote:
I'd say we need a better definition of "snappy"...

I'll see if NIST has one we can reference.

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 Post subject:
PostPosted: Fri Sep 07, 2007 9:26 pm 
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Joined: Sun Mar 18, 2007 12:38 am
Posts: 15
Quote:
I'd say we need a better definition of "snappy"...


dictionary.com's 4th entry is sufficient:

Quote:
4. quick or sudden in action or performance.


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 Post subject:
PostPosted: Fri Sep 07, 2007 11:58 pm 
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Joined: Wed Mar 03, 2004 7:43 pm
Posts: 748
Location: Sydney, Australia
beerisgoodmate wrote:
Some times it sits there for a few seconds with rapid HD activity, could this be due to running out of ram and using swap?


Unlikely. My home Myth box originally had 256MB (R4V4?). It never used swap very much. Newer MythTV versions, and complicated menu themes, use a little bit more RAM, but not a lot.


Changing channels in LiveTV just takes a long time. A fast hard disk, or a faster filesystem, helps a little bit. Turning down the "HD Ringbuffer size" helps a tiny bit (if it is ridiculously large).

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| "Things you own end up owning you" - Tyler, Fight Club


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 Post subject:
PostPosted: Sat Sep 08, 2007 2:48 am 
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Joined: Mon May 10, 2004 8:08 pm
Posts: 1891
Location: Adelaide, Australia
I have a default partition setup (ext3 for /myth) and when files are deleted, it can cause significant pauses. Is it possible that it is shows auto-expiring that are causing the pauses? Is your HD almost full? I have heard some claim that changing the filesystem type for the /myth partition to a filesystem with snappier deleting of large files can help in this regard.


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 Post subject:
PostPosted: Sat Sep 08, 2007 11:47 pm 
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Joined: Sun Mar 18, 2007 12:38 am
Posts: 15
hmmm,

I added a 320Gb seagate SATA (limited to sataI), formated as one XFS partition and set the partition to store tv.

Now my channel changes are slower!

I also added a DTV2000H card at the same time though. And I'm not sure if things are quite right.

Old channel changes on DTV1000T ~3.6 s

New channel changes DTV2000H ~4.4 s
New channel changes DTV1000T ~6s

Not sure if everything is set up correctly with the new card and remote yet... But I think those numbers are ok.

edit:
I think some of the slowdown was changing myth's tv partition, it kept looking for expired recordings to delete.

I fixed this, this improves speed a little, but it is still slower.


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