[mythtv-users] diskless xBox stuttering - was Help Diskless frontend

[Cymen Vig]

On 11/7/05, Ben Dash <ben_dash at yahoo.com> wrote:
>
> --- George Nassas wrote:
> > On 5-Nov-05, at 10:20 PM, Ben Dash wrote:
> > > since I changed to a 2.6 kernel I get no errors
> > I'm running 2.4 because I read the 2.6 fatx driver
> > isn't quite ready
> > for prime time. Do you do any updating of the xbox's
> > filesystem while
> > you're in linux?
>
> No.  The only thing I'm using the native HDD for is
> swap and that seems fine with the fatX drivers for
> 2.6.  I read somewhere that a major problem with FatX
> for 2.6 was a lack of long filename support and swap
> doesn't need that.
>
> > > I just don't understand why I'm getting stuttering
> > > when my CPU utilization is so low, i.e. 50%.  I
> > had a
> >
> > Could it be something to do with syncing updates to
> > the vertical
> > retrace? I've never had those kinds of issues on any
> > of my FEs but I
> > think some past threads on this list that mentioned
> > that. One of those
> > things you skim and file away for future use. Look
> > for Use OpenGL VSync
> > in the TV Playback menus.
> >
> > BTW, does the frontend log say anything?
>
> The frontend log just says "prebuffering pause".
>
> I had an interesting development this weekend, I would
> have replied to this thread earlier but my PC was in
> pieces for an upgrade.  Anyway, my development was
> that I found that if I run an xterm in the background
> and run top on it, then I get hardly any "prebuffering
> pause" stuttering.
>
> The stuttering goes from once every 10 seconds,
> without the xterm runing top, to once every 10 minutes
> with the xterm running top.  Interestingly, when a
> stutter occurs the CPU utilization appeared to go down
> not up.  Clearly the CPU isn't the limiting factor in
> this case.
>
> I have a gigabit switch so I doubt that I have a
> network bandwidth problem.  My myth backend server is
> a different machine than my NFS root server (note that
> the xBox frontend is diskless with an NFS root except
> for a local fatX swap).
>
> So, the current status is that I, and more importantly
> my wife, can experience stutter free live TV and
> recorded shows at 640x480, which is GREAT.  All I have
> to do is start up an xterm running top in the
> background.
>
> This seems more than a little wierd though.
>
> Does anyone have any idea why this solution is able to
> mask the problem and, if so, what a real solution
> could be?

That is definately bizarre -- I don't have any idea why that is
happening. I did wonder if you had run "chmod a+s mythfrontend" and
selected the option to have realtime priority in MythTV (I think it's
in Settings->Play TV) and verified it is using realtime priority by
looking at the frontend log? I realize the CPU usage goes down when it
occurs but I am curious all the same. If you don't want to deal with
the above you could also start playback and then adjust the priority
of the specific playback process to see if it changes anything.