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Thread: Video stuttering: messages about RingBuf, video buffers

  1. #1
    Join Date
    Aug 2011
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    32

    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?

  2. #2
    Join Date
    Jul 2012
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    63

    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.

  3. #3
    Join Date
    Aug 2011
    Beans
    32

    Re: Video stuttering: messages about RingBuf, video buffers

    Thanks for the reply.

    Quote Originally Posted by Rotak View Post
    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 View Post
    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?

  4. #4
    Join Date
    Jul 2012
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    63

    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

  5. #5
    Join Date
    Aug 2011
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    32

    Re: Video stuttering: messages about RingBuf, video buffers

    Quote Originally Posted by Rotak View Post
    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:


    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?

  6. #6
    Join Date
    Jul 2012
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    63

    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.

  7. #7
    Join Date
    Aug 2011
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    32

    Re: Video stuttering: messages about RingBuf, video buffers

    Quote Originally Posted by Rotak View Post
    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

  8. #8
    Join Date
    Jul 2012
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    63

    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.

  9. #9
    Join Date
    Mar 2007
    Location
    Christchurch, NZ
    Beans
    3,239

    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).

  10. #10
    Join Date
    Mar 2007
    Location
    Christchurch, NZ
    Beans
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    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?

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