Intel Core i3, LMDE, jittery HD performance

Have a MythTV related problem? Ask for help from other MythTV users here.

Moderator: Forum Moderators

Post Reply
rodr
Newcomer
Posts: 13
Joined: Sun Apr 12, 2015 5:57 pm
Australia

Intel Core i3, LMDE, jittery HD performance

Post by rodr » Thu Dec 24, 2015 4:39 pm

I've got a PC with a Core i3 CPU running Linux Mint Debian Edition and the MythTV 0.27.5 that comes with it. Backend and frontend are installed as well as Kodi. The backend records DirecTV SD as well as OTA. Recordings are stored in a 1.4 TB JFS partition on a 2 TB hard drive.

The problem is that HD (from OTA recordings) playback is jittery. I set up VAAPI using the instructions at https://www.mythtv.org/wiki/VAAPI and that helped, with about 6-8% CPU utilization during playback. I also set up real time threads but don't know how to tell if that's working. The Kodi mythtv client plays the same recordings just fine, no jitter at all.

But with the MythTV frontend there's still jittery video in scenes where most of the screen area is moving. While CPU load is low, "top" shows high wait ("wa") times, around 50-80%. So it's spending a lot of time waiting for I/O completion. Kinda sounds like the bottleneck is disk performance? But if that's true why doesn't Kodi have a problem?

Thanks in advance for any thoughts and suggestions.

rodr
Newcomer
Posts: 13
Joined: Sun Apr 12, 2015 5:57 pm
Australia

Re: Intel Core i3, LMDE, jittery HD performance

Post by rodr » Fri Dec 25, 2015 9:28 pm

No ideas yet?

A bit more info...

The drive is a Samsung HD204UI internal SATA.

I have tried Disabling file access time logging without any noticeable improvement. Same non-result with "sudo blockdev --setra 1024 /dev/sda".

Kwisher
Junior
Posts: 58
Joined: Fri Sep 25, 2015 3:02 pm
United States of America

Re: Intel Core i3, LMDE, jittery HD performance

Post by Kwisher » Sat Dec 26, 2015 5:54 pm

Sounds like a frontend playback issue to me if video plays fine with another application. Go to the frontend menu>setup>video>playback and on the 3rd screen change the profile until you find one that works. There is a profile for VAPPI Normal, which you mentioned you already setup in your original post.

rodr
Newcomer
Posts: 13
Joined: Sun Apr 12, 2015 5:57 pm
Australia

Re: Intel Core i3, LMDE, jittery HD performance

Post by rodr » Sat Dec 26, 2015 6:53 pm

Thanks for the response. Some interesting developments...

First, I noticed today that the kernel was running only a single CPU on my i3. Seems LMDE installs a kernel for older CPUs by default with no SMP support. So I installed a more suitable kernel and rebooted.

With high hopes I tested HD playback again. No luck, still choppy.

Then I changed the playback profile from "VAAPI Normal" to just "Normal". Success!

CPU usage is high again as you would expect with no VAAPI, but with both cores active now it's keeping up. Also the CPU wait time percentage went WAY down, from 50-80% to less than 1%.

Bottom line: Something's wrong with VAAPI support. I wonder if it's the GPU that was not keeping up, causing the high wait times?

User avatar
dekarl
Developer
Posts: 228
Joined: Thu Feb 06, 2014 11:01 pm
Germany

Re: Intel Core i3, LMDE, jittery HD performance

Post by dekarl » Sun Dec 27, 2015 9:24 am

rodr wrote:playback is jittery....
But with the MythTV frontend there's still jittery video in scenes where most of the screen area is moving....
No luck, still choppy....
Can you give an example of the visual effect that you call jittery / choppy?
Is it tearing, where you see part of the screen of an earlier image and the rest of the screen a later image?

It may also be judder due to non-matching frame rates. But if switching between "normal" and "VAAPI normal" makes a difference then I'm betting on the former.
It appears that others have a similar issue with VAAPI.

rodr
Newcomer
Posts: 13
Joined: Sun Apr 12, 2015 5:57 pm
Australia

Re: Intel Core i3, LMDE, jittery HD performance

Post by rodr » Sun Dec 27, 2015 12:59 pm

Not tearing, and didn't look like anything to do with mismatched frame rates. I would call it dropped frames, or intermittent freezing of the display. It happens when most of the screen area is changing, as in panning or zooming, which I guess is when the bitrate is higher.

I also just tried it with "OpenGL Normal" as the playback profile and the effect was similar but worse, happening even with a talking head on a static background.

rodr
Newcomer
Posts: 13
Joined: Sun Apr 12, 2015 5:57 pm
Australia

Re: Intel Core i3, LMDE, jittery HD performance

Post by rodr » Sun Dec 27, 2015 8:41 pm

I think what's going on here is that my i3 is a Clarkdale, which is first generation and does not have the on-chip support for video decoding that was introduced with the subsequent Sandy Bridge version (which has about double the video performance). Seems like MythTV should handle its limitations more gracefully, but at this point I can play my HD recordings smoothly without VAAPI and won't worry about it further,

Thanks to Kwisher and dekarl for your input.

Kwisher
Junior
Posts: 58
Joined: Fri Sep 25, 2015 3:02 pm
United States of America

Re: Intel Core i3, LMDE, jittery HD performance

Post by Kwisher » Tue Dec 29, 2015 2:41 pm

Can you add a nVidia GPU to offload playback to it rather than the CPU?

rodr
Newcomer
Posts: 13
Joined: Sun Apr 12, 2015 5:57 pm
Australia

Re: Intel Core i3, LMDE, jittery HD performance

Post by rodr » Tue Dec 29, 2015 4:27 pm

Kwisher wrote:Can you add a nVidia GPU to offload playback to it rather than the CPU?
Yes I'm sure a separate video card is an option, and may be necessary if I move to a higher resolution TV (currently using a 720p plasma TV).

Post Reply