Note: I am posting here rather than in "hardware" or "linux" because I believe that the situation I am describing doesn't typically apply to non-HD systems.

I just upgraded my system from 512MB of PC3200/Corsair/CAS2.5 memory to 1GB of PC3200/Corsair/CAS3 memory. The most notable difference is visibile when I am simultaneously recording and playing back the same 1080i hidef show and also recording the same show at 480i.

1. With 512MB CAS2.5 memory, "top" typically shows 20% - 30% of CPU in the "wa" state, and I run around 20% "idle".

2. With 1GB of CAS3 memory, "top" consistantly shows under 1% in the "was" state and I run 40% - 50% idle.

So while I am very happy with the new results, I am trying to understand why. I've done some reading on CAS latency and I doubt having a longer/worse latency would somehow make things better, so my guess is that the benefit is coming from having more memory.

Does anyone out here have any inisghts? It's not a problem, but I am very curious.

Marc

System configuration:

Knoppmyth R5A30.2
P4-2.8ghz w/ HT.
1GB RAM
ECS motherboard with SIS chipset

Are you commflagging at the same time as recording? I found my memory requirements were pretty high in this scenario. I started with 512M and found that 1G was a real help as well. Back when I had only 512M I found that turning off commflagging helped memory utilization.

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No, I don't use commflag and I did not have any jobs running in the background.

I just ran into something really similar. I bumped from 512MB to 1.5G, and the playback stream got MUCH more stable. It looks like it just needs the added workspace in physical RAM for temporary manipulation of the video stream, whether it be the frontend, backend, X, the DVB driver, or some combination of the 4. It's just a whole lot more happy with more memory.

The other thing that could have happened is that by introducing the second DIMM you enabled a dual-chanel feature some motherboards have, thereby drastically reducing latency through the resultant alternating access to the DIMMs.

Just a thought... which mobo brand/model are you using?

Regards,
Paul

mudx, sounds like we are seeing the same result.

aussiepoof, I upgraded by replacing my single 512MB DIMM with a single 1GB DIMM, so I don't have dual channel access. My MOBO is an ECS 648FX-A.

Marc

That's the thing. With both the Athlon 3200 and then the 3800X2 under the hood, both were running a pair of 256 sticks in dual channel mode. When I put the additional memory in, it was a pair of 512 sticks, also in dual channel mode. It doesn't seem like it was an issue of the width of the pathway so much as how much memory the kernel's got to play with.

Cross-ref thread: http://mysettopbox.tv/phpBB2/viewtopic.php?t=10105

That does indeed seem a reasonable conclusion... and I have noticed Myth sucks memory hard.

P.

I have an Athlon 64 3000+ with 512Mb of single channel ram and no performance issues. Ok i'm running SDTV not HDTV, but I can record 2 channels whilst watching something else. Most memory is in cache and buffers.

If I go HD I might consider an additional 512MB stick.

Why to people think "MythTV sucks memory hard"?

Steve

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I don't know, but I have 512Mb ram and I use HD with no problems. I can record two hd streams and one sd stream while watching hd no problems. Not sure what's the issue for everyone else. Though I do have commflag turned off. That is guaranteed to screw up playback when an hd recording is commflagging.

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What's the spec on your system?

PIV 3.0g ht with 512Mb ram gf5200 (well old gf3 right now since my 5200 blew up) connected dvi to hdtv at 1080i (720p right now since gf3 can't do interlace)

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