[mythtv] weird pdflush & NFS problem

Mark Lehrer mark at knm.org
Tue Feb 6 17:27:37 UTC 2007

On Tue, Feb 06, 2007 at 09:36:31AM -0500, Dan Wilga wrote:
> At 2:15 PM -0700 2/5/07, Mark Lehrer wrote:
> >I have been having some issues with MythTV - whenever it is recording
> >a hi def show and playing something back at the same time, there are
> >pauses every 30 seconds or so.  These pauses happen when pdflush wakes
> >up to write out the disk cache.
> I had a similar problem, and was able to minimize its impact by 
> actually decreasing the write buffer size of the mounted volume, so 
> that it writes more frequently. In /etc/fstab, if you have something 
> like:

Thanks for the suggestions, I'll be trying those as well as
adjusting some kernel settings such as /proc/sys/vm/dirty_expire_centisecs

However, the reason I posted here is that I think the ring buffer
feature is either broken or I misunderstood it - does MythTV try to
read ahead by this amount of data?  If so, this feature doesn't seem
to be working.  A pdflush on the NFS server causes an instant pause in
the MythTV backend.  A feature similar to mplayer's -cache option
would be a good idea to avoid these kinds of problems.


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