[mythtv-commits] Ticket #7605: Jumpy DVD playback - lock contention

[MythTV]

#7605: Jumpy DVD playback - lock contention
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 Reporter:  john.p.harvey@…               |       Owner:  janne  
     Type:  defect                        |      Status:  new    
 Priority:  minor                         |   Milestone:  unknown
Component:  MythTV - Video Playback       |     Version:  head   
 Severity:  medium                        |     Mlocked:  0      
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 I have a problem playing back dvd's on a low powered system. Dual Core
 Atom using vdpau graphics.
 If the DVD's are imported and played from disk (local or network) it is
 fine.
 The playback is very jumpy and after digging around the problem is caused
 by locking in dvdnav between avformatdecoder & dvdringbuffer.

 Both call IsInMenu which calls into dvdnav_is_domain which does a lock.
 For some reason avformatdecoder fails to get the lock for up to about a
 second which causes the jumpy behaviour.

 Just before calling that it avformatdecoder cals DVD()->CellChanged() &
 DVD->InStillFrame() which are stored in DVDRingBuffer & don't do any
 locking.

 As a test i modified IsInMenu to cache the state and only call dvdnav to
 update the cached value from methods in DVDRingBuffer that fetch new data.

 Since avformatdecoder doesn't try to get a lock this seems to fix the
 problem but could someone confirm whether or not this change seems
 reasonable? If so i will submit a patch.

 This doesn't really explain why avformatdecoder was being starved of the
 lock in dvdnav but i nothing seems to change that,(enable/disable real
 time threads, different sync methods, enable/disable hyperthreading).
 I am running on ubuntu 9.10.

 I have attached the patch i am using which definately helps with the
 problem but may not be a good solution

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Ticket URL: <http://svn.mythtv.org/trac/ticket/7605>
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