[mythtv-users] MythTV problems with 3.7.x and 3.8.x kernel

[Karl Newman]

On Sat, Feb 23, 2013 at 6:15 PM, Neil Salstrom <salstrom at gmail.com> wrote:

> On Fri, Feb 22, 2013 at 11:29 PM, Neil Salstrom <salstrom at gmail.com>
> wrote:
> > Has anyone else noticed problems watching DVD's using a 3.7.x kernel
> > or a 3.8.x kernel?  I first noticed the problem a while back and
> > started this thread:
> >
> >
> http://www.gossamer-threads.com/lists/engine?do=post_view_flat;post=537334;list=mythtv
> >
> > It seemed to be related to using the 3.7 series kernel at that time
> > but now with 3.8 out I get the same problem.  It only affects (as far
> > as I can tell) DVD's played from the physical disk or a full .iso of
> > the physical disk.  A .mkv from the main feature has no problems.
> >
> > Switching back to a 3.6.x kernel or earlier fixes the problem.  Oddly,
> > I can only get the issue to happen in MythTV and not in any other
> > playback program.  It happens regardless of playback method as well
> > (VDPAU, OpenGL, etc).  This evening I tried a self compiled 3.8.0
> > kernel as well as a generic 3.8.0 .deb kernel from Ubuntu.
> >
> > Looking at the 3.7 change log the only thing that sticks out is:
> >
> > Filesystems:
> > UDF:
> >
> > Add support for O_DIRECT
> > Add "writepages" support for UDF for improved write performance
> >
> > Could either O_DIRECT or writepages cause this?  I know nothing about
> > this topic so I'm just stabbing in the dark here.  Anyone have any
> > ideas?  Any way to turn off these two items in 3.8.0 to test?
> >
> > Thanks,
> >
> > Neil
>
> Ok, I tried an experiment by compiling 3.8 using the 3.6.11 UDF files
> which were changed starting in 3.7:
>
> arch/um/os-Linux/time.c
> fs/udf/file.c
> fs/udf/inode.c
>
> This removed both the support for O_DIRECT and writepages in my
> compiled 3.8.0 kernel.  It compiled and installed successfully.
> Sadly, it did not fix the stuttering issues.  Moved back to 3.6.11 and
> all is fine...
>
> Not sure where to go from here.  I'm focusing on the UDF portion of
> the kernel because it only affects DVD's and nothing else.
>
> Suggestions on trying to figure out why 3.7 or above breaks DVD playback?
>
> Thanks!
>

Since you're set up to compile and use your own kernel, you might try a
bisect to find the offending commit. Here's the documentation:
http://www.kernel.org/pub//software/scm/git/docs/git-bisect.html In your
case you should start with the first 3.6.0 kernel and the first "bad" 3.7
kernel (3.7.0?). Based on my limited knowledge about kernel development
practices, I believe that will minimize the number of commits between the
good and bad trees. Ideally you would find a bad commit which could be
reported upstream to the linux kernel list, but if they don't confirm it as
a bug, at the least you could create a reverse patch that you could apply
which would remove the problematic commit for your custom kernel and then
the mythtv devs could look at it on their end. I've done this once and it
took about 12 iterations to find the commit which caused my problem (not
mythtv related).

Karl
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