[mythtv-users] NVP: prebuffering pause -- what does it mean, really?

Willy Boyd willyboyd at gmail.com
Mon Mar 19 14:05:07 UTC 2007

On 3/17/07, Willy Boyd <willyboyd at gmail.com> wrote:
> At this point I have had liveTV running for almost 11 hours straight.
> I have been asleep most of that time, but in the mythfrontend log
> (back to "normal" log level, no switches), I see that it went from
> 12:30AM until 10:50AM with no messages -- which is when I changed the
> channel, and did get one pair of "prebuffering pause / Prebuffer: wait
> timed out 10 times" messages.  No visible hiccup though, and I'm going
> to leave it here a few more hours and see how it plays.
> Last night I turned GLX back on (because it hadn't helped), and I
> tuned my mysql config.  I think this may have been what really helped,
> but we'll see.  This is what I added to the mysqld section of
> /etc/my.cnf (based on what I found searching the list archive):
> key_buffer = 16M
> max_allowed_packet = 8M
> table_cache = 128
> sort_buffer_size = 16M
> net_buffer_length = 8M
> thread_cache_size = 4
> query_cache_type = 1
> query_cache_size = 4M
> As a side effect, this makes mythweb much speedier due to query
> caching.  But only time will tell if this is the true fix for my
> freezing.  OH, and I checked temps, and my cores never go above 48
> celcius during playback.  So I ran a myth svn compile, and they maxed
> at 58 celsius, tops.  And this is still with cpuspeed disabled.

Just replying to myself here to followup.  The same continued
throughout the weekend -- we had liveTV going for close to 24 hours as
of Saturday, and off and on Sunday.  The only time I saw the
pause/timeout messages was immediately after a channel change, with no
visible hiccup.  Then it would continue on just fine until another
channel change (i.e., no problem across program changes).

I can't say *for sure* that the cpuspeed governor being off has no
effect, because though I did experience the one crash after disabling
it -- that filled my log with "LiveTV forcing JumpTo 1" messages -- I
had to delete that 1.7GB logfile because I got scared that there was 0
bytes left on my root partition.  So I really don't know what happened
there.  I'm leaving cpuspeed off for good measure -- at least for a
few days then I might test with it on again.

However, the mysql tuning can only be a good thing regardless, and I
put more weight on that being the big helper.  I consider it something
that "fixes the symptoms", but not necessarily a cure.  My last
hardware was much weaker, and I never knew about mysql tweaking, yet
it played SD like a champ.  This setup is much beefier.  Something has
changed in code, that is either less efficient or just does more work
than before (I basically upgraded everything, I consider this
basically a new install).  I'm happy with things as they are now, and
looking forward to HD!

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