Video stuttering: messages about RingBuf, video buffers

I'm having playback issues on a combined frontend/backend myth system. I've been using MythTV for about three years now with no playback issues. I've upgraded hardware several times, most recently replacing a single WD20EARS with an SSD for the system and a WD20EARX for videos. Now I get errors like this during video playback or while watching live TV:

Code:

Sep 29 21:40:22 mythtv mythfrontend[8385]: I Decoder ringbuffer.cpp:1086 (WaitForAvail) RingBuf(/second_drive/recordings/3130_20120103210000.mpg): Waited 2.0 seconds for data #012#011#011#011to become available... 0 < 32768 Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 3719ms for video buffers AAAAAAAAAAALff Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 3823ms for video buffers AAAAAAAAAAALff Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 3926ms for video buffers AAAAAAAAAAALff Sep 29 21:40:22 mythtv mythfrontend[8385]: N CoreContext mythplayer.cpp:2078 (PrebufferEnoughFrames) Player(g): Waited 4029ms for video buffers AAAAAAAAAAALff

If a recording is being made while watching a different recording or live TV the problem is exacerbated.

Ubuntu 12.04.1 LTS (GNU/Linux 3.2.0-31-generic-pae i686)
MythTV Version : v0.25.2-15-g46cab93
MythTV Branch : fixes/0.25
Playback is set to VDPAU slim
Combined frontend/backend on
Intel i5-2400S
ASUS ENGT520 SL/DI/2GD3
Crucial CT64M4SSD2
Western Digital WD20EARX
I searched for related issues and found several threads, most nearly a year old, regarding various issues like playback from a NAS, using multiple frontends, etc. But none of the cases I've found represent my situation.

What might cause these issues?

Re: Video stuttering: messages about RingBuf, video buffers

What filesystem are you using?

A friend of mine had issues about R/W speed with an SSD drive. A BIOS update fixed that. No idea if your issue could be related to BIOS as well.

Re: Video stuttering: messages about RingBuf, video buffers

Thanks for the reply.

Quote:

Originally Posted by Rotak

What filesystem are you using?

The operating system ('/') resides on an ext4 partition on the SSD. All recordings are written to an XFS partition on the 2 TB WD drive.

Code:

$ df Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda2 57927924 6128544 48856816 12% / udev 2047276 4 2047272 1% /dev tempfs 2054548 3788 2050760 1% /tmp tmpfs 821820 1064 820756 1% /run none 5120 4 5116 1% /run/lock none 2054548 148 2054400 1% /run/shm /dev/sdb1 1952559608 881549900 1071009708 46% /second_drive $ sudo parted /dev/sda GNU Parted 2.3 Using /dev/sda Welcome to GNU Parted! Type 'help' to view a list of commands. (parted) print Model: ATA M4-CT064M4SSD2 (scsi) Disk /dev/sda: 64.0GB Sector size (logical/physical): 512B/512B Partition Table: gpt Number Start End Size File system Name Flags 1 17.4kB 1018kB 1000kB bios_grub 2 1018kB 60.3GB 60.3GB ext4 3 60.3GB 64.0GB 3758MB linux-swap(v1) $ sudo parted /dev/sdb Using /dev/sdb Welcome to GNU Parted! Type 'help' to view a list of commands. (parted) print Model: ATA WDC WD20EARX-008 (scsi) Disk /dev/sdb: 2000GB Sector size (logical/physical): 512B/4096B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 2000GB 2000GB primary xfs

Quote:

Originally Posted by Rotak

A friend of mine had issues about R/W speed with an SSD drive. A BIOS update fixed that. No idea if your issue could be related to BIOS as well.

I haven't looked for motherboard BIOS updates recently but last time I checked I was at the latest version. The MB is an ASUS P8H67-M PRO/CSM. Checking the website just now, it appears there are no downloads (BIOS or otherwise) which, presumably, is either a bug or an indication that the product is deprecated (http://usa.asus.com/Motherboards/Int...OCSM/#download).

Were your friend's recordings written to the SSD?

Re: Video stuttering: messages about RingBuf, video buffers

I will ask my friend. I know it was an ASUS board, too.

He changed his setup a few months ago. He's now only writing LiveTV to the SSD and is storing recordings on a NAS.

Maybe you can "benchmark" your HDDs by using:

Code:

sudo hdparm -tT /dev/sda

(and sdb, of course)

Here is the output of my myth server, while I was watching TV (system not idle):

Code:

sudo hdparm -tT /dev/sda /dev/sda: Timing cached reads: 14488 MB in 2.00 seconds = 7252.89 MB/sec Timing buffered disk reads: 166 MB in 3.02 seconds = 54.88 MB/sec

Re: Video stuttering: messages about RingBuf, video buffers

Quote:

Originally Posted by Rotak

Maybe you can "benchmark" your HDDs by using:

Code:

sudo hdparm -tT /dev/sda

(and sdb, of course)

Cool utility...I didn't know there was a quick way to check disk performance.

Here are some results:
http://i1075.photobucket.com/albums/...erformance.jpg

Looks like (by this metric at least) there should be sufficient throughput on /dev/sdb and the SSD on /dev/sda appears to perform as expected for an SSD.

On a whim, I watched atop while viewing a recording and another one was being written to disk. I saw this during smooth playback:

Code:

DSK | sdb | busy 17% | read 70 | write 47 | KiB/r 244 | | KiB/w 357 | MBr/s 1.67 | MBw/s 1.64 | avq 1.49 | avio 14.7 ms |

When a playback stall occurred, I saw this:

Code:

DSK | sdb | busy 98% | read 22 | write 7 | KiB/r 302 | | KiB/w 258 | MBr/s 0.65 | MBw/s 0.18 | avq 6.74 | avio 334 ms |

Obviously the busy percentage is a problem. The other obvious issue is avio (far right, you have to scroll over in the code section of the post), which I assume is some measure of access time based on its healthy number.

I've never seen anything like this before. Any thoughts on what might cause intermittent high disk latency?

Re: Video stuttering: messages about RingBuf, video buffers

Phew. I experimented with file systems a long time ago (Mythbuntu 10.04).

With kernel 2.6, I (sooner or later) experienced speed problems with any journaling file system. Therefore, I switched to ext2.

Maybe a filesystem geek could comment this. 8-[

Re: Video stuttering: messages about RingBuf, video buffers

Quote:

Originally Posted by Rotak

With kernel 2.6, I (sooner or later) experienced speed problems with any journaling file system. Therefore, I switched to ext2.

Huh...hadn't considered that angle. In hopes of expert filesystem insight, here's my fstab (parameters for the XFS partition that all recordings go on are "defaults"):

Code:

$ cat /etc/fstab # /etc/fstab: static file system information. # # Use 'blkid' to print the universally unique identifier for a # device; this may be used with UUID= as a more robust way to name devices # that works even if disks are added and removed. See fstab(5). # # <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc nodev,noexec,nosuid 0 0 UUID=0efa47e2-b174-49be-8726-dfcca4fb9c10 / ext4 errors=remount-ro 0 1 UUID=e728f64d-4c7a-4d1a-bd1a-efce96c6274e none swap sw 0 0 tempfs /tmp tmpfs nodev,nosuid 0 0 UUID="35fa6798-8564-46e2-8714-6c5385df220b" /second_drive xfs defaults 0 0

Re: Video stuttering: messages about RingBuf, video buffers

I am hesitant to give any advice on XFS mount options or on using and fs-tools to set options, because I have no XFS partition running.

As far as I remember, it's not possible to turn off journaling on XFS. But maybe somebody knows other optimization options. I read of some optimizations, but those have to be done when creating the filesystem. :(

Re: Video stuttering: messages about RingBuf, video buffers

It is unlikely that your filesystem is to blame. There was a bug I saw fixed for 0.26 about the livetv buffer being out by a factor of 10 (ie 1/10th the size it should have been). I recall seeing the fix committed for 0.26, not sure if it was for 0.25 or 0.24. I cannot find the damned commit now and therefore can't confirm.

Try pausing, let the buffer build up a bit and restart. Should only take a short pause. If that works we have probably at least found the bug, even if the workaround is a PITA. (albeit an easy to implement PITA).

Re: Video stuttering: messages about RingBuf, video buffers

Got it, it's ticket 10428 in track and commit 483e06f in git. Unfortunately not backported to 0.25 so far as I can see.

http://code.mythtv.org/trac/ticket/10428

https://github.com/MythTV/mythtv/com...a5f844519f51f9

Time to try 0.26?