Mailing List Archive: MythTV: Dev

weird pdflush & NFS problem

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mark at knm

Feb 5, 2007, 1:15 PM

Post #1 of 3 (422 views)
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weird pdflush & NFS problem

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.

Does MythTV have an option that works the same way as mplayer's -cache
option? I thought that the ringbuffer setting would be the same.
Obviously it isn't, because MythTV is pausing instantly once the NFS
server decides to take a break for a couple of seconds.

Thanks,
Mark

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mythtv-dev2 at dwilga-linux1

Feb 6, 2007, 6:36 AM

Post #2 of 3 (390 views)
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Re: weird pdflush & NFS problem [In reply to]

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:

hostname:/foo /mnt/foo nfs
rw,nosuid,soft,rsize=8192,wsize=8192,retry=1,bg,actimeo=0,async,nfsvers=3
0 0

Try changing "wsize" to a smaller number:

hostname:/foo /mnt/foo nfs
rw,nosuid,soft,rsize=8192,wsize=2048,retry=1,bg,actimeo=0,async,nfsvers=3
0 0
--
Dan Wilga "Ook."
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mark at knm

Feb 6, 2007, 9:27 AM

Post #3 of 3 (384 views)
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Re: weird pdflush & NFS problem [In reply to]

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.

Thanks,
Mark

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