[mythtv-users] mythfronend stuttering

[Tony Lill]

It may not have anyting to do with hardware or myth, and have
everything to do with the kernel.

When I switched from 2.4.26 to 2.6.14, I ran into problems with
stuttering. I had my kernel configured for 1000Hz and full pre-emption
originally, and it would often get into a state where it would pause
for about a second every few seconds.

I switched the kernel to 250Hz and voluntary pre-emption and it seemed
to help a little. Eventually, I realized that what was happening was
that when it flushed it's dirty buffers to disk, playback would
pause. What finally seemed to fix it was:

# % of physical memory after which a process doing a write will be paused
# untill dirty pages have been written
# default 40
echo 50 > /proc/sys/vm/dirty_ratio

# % of physical memory at which pdflush will be woken. Hopefull this will limit
# system pauses for flushes
# default 10
echo 5 > /proc/sys/vm/dirty_background_ratio

I think that if you have too much memory, and an otherwise idle
system, the disk flushes can get big enough to starve the
frontend. Try re-compiling the kernel next time it starts
stuttering. If the disk i/o it causes smooths out your playback, you
know that's your problem.

I was thinking of starting a new thread here on what people think the
best config/tuning is on 2.6.14, since out of the box it's been a lot
of trouble.

Raphael Pooser <rpooser at gmail.com> writes:

> Chad wrote:
>
>>>>Well, there's some info missing here that might help ;)
>>>>
>>>>What CPU, videocard, soundcard and how are all these setup (if
>>>>videocard is NVidia, what drivers, and are you using xvmc...).  :)
>>>>
>>>>Also, on the Gentoo note, I use the SVN-ebuilds most the time (though
>>>>occasionally I forget I have them and grab the latest SVN source and
>>>>compile by hand :D ).
>>>>
>>>>Chad
>>>>_______________________________________________
>>>>mythtv-users mailing list
>>>>mythtv-users at mythtv.org
>>>>http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>>>>
>>>>
>>>>
>>>>      
>>>>
>>>What is xvmc?
>>>    
>>>
>>
>>Xvideo Motion Compensation.  In lamen terms it offloads the video to
>>the graphics processing unit (GPU) from the CPU.  It's drawback is
>>that it generally only does mpeg2 decoding.
>>
>>  
>>
>>>Is it really a good idea to use the trunk for something that's as
>>>complete as mythtv? (I can understand using the trunk for something
>>>pre-alpha.)
>>>    
>>>
>>
>>Not always no.  I think a lot of people on here suggest the Trunk
>>because it's been a fair amount of time since the last stable release
>>(which is a better guideline as to whether or not to use SVN/CVS or
>>the official release).  However, it's not absolutely necessary, it's
>>just that there are some really good code updates/upgrades/additions
>>in the SVN release that may make your system play nicer than the
>>latest release (currently 0.18.x).
>>
>>  
>>
>>>Here are the specs of the computers:
>>>
>>>The computer running mythbackend:
>>>Asus K8N-E (nForce4 Ultra)
>>>AMD Athlon 64 3700+ s939
>>>1GB PC3200 (2x512MB)
>>>nVidia GeForce 6600
>>>Using onboard sound
>>>Using onboard ethernet (forcedeth)
>>>Gentoo i686 w/ linux-2.6.15-ck1
>>>    
>>>
>>
>>Sounds nice, also sounds like a TON of overkill in areas that don't
>>need it if this is JUST a backend. :)
>>
>>  
>>
>>>My Computer:
>>>Asus K8V-X (Via K8T800)
>>>AMD Athlon 64 3000+ s754
>>>1GB PC3200
>>>nVidia GeForce 6800GT 256MB
>>>M-Audio Revolution 7.1
>>>Using onboard ethernet (marvel 88NE8001)
>>>Gentoo i686 w/ linux 2.6.14-ck6
>>>    
>>>
>>
>>Certainly sounds like a decent enough system, as long you look into
>>and use XvMC, you should be able to playback mpeg2 content without
>>'stutter'.
>>
>>  
>>
>>>Switch: Dlink DGS-1005D (both connected with Cat5e, speed is around
>>>250-280Mb/s)
>>>_______________________________________________
>>>    
>>>
>>
>>Good Luck!
>>
>>Chad
>>_______________________________________________
>>mythtv-users mailing list
>>mythtv-users at mythtv.org
>>http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>>
>>  
>>
> Reuben,
> Just to second most of what Chad said, except the part about updating 
> your mythtv version.  There are some nice updates to the code, but most 
> likely the stuttering has nothing to do with what version of myth you're 
> using, and everything to do with your graphics card drivers.  Check your 
> processor usage (typing "top" at the command line or however you want to 
> do it) and most likely you'll see that you're near 100% usage on your 
> processor while playing back video.  It'd be easiest to ssh into the 
> machine to check it while video is running, because if you do it on the 
> machine itself the usage will go down everytime you switch out fo the 
> video. Anyway, the processor utilization depends on resolution in the 
> case that you're not using xv or xvmc, and probably you're trying to 
> watch 640x480 or higher resolution files.  Just make sure your graphics 
> card drivers are installed correctly (make sure the module's loading and 
> that X doesn't give you a message like "incorrect kernel module, no 3d 
> acceleration is available."  Then make sure the option to enable xvmc is 
> enabled in xorg.conf. or xf86config-4.
> I had the same problem with an ATI card and xv, and had the exact same 
> type of stuttering as you.  Once I got xv working there was a night and 
> day difference.
> I would say try and get xvmc working first, then worry about upgrading myth.
> Raphael
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