[mythtv] Re: Solving my performance problems...

[Mark Frey]

Bruce Markey wrote:
>> Perhaps on a machine heavily CPU limited this would help. Does anyone
know
>> why this was added? Without it performance is much better (on my machine
of
>> course, YMMV).
>
>Not sure how you are gaging performance. For me it didn't
>increase CPU load or anything like that but it did reduce
>jitter. If you have some metric where there is clearly a
>negative impact I'd certainly like to look into it.

My hardware is hard-drive-throughput limited, so starving the read thread
hurts performance for me. I measure net hard drive throughput (bytes read by
the read ahead thread over time) and I lose about 15% with the sched_yield()
in there.

>On the very first attempt, it paused several times and failed
>within 20sec.
>
>Frontend:
>
>2003-12-17 18:05:39 Connecting to backend server: 192.168.0.35:6543 (try 1
of 1)
>2003-12-17 18:05:44 Opening OSS audio device '/dev/dsp'.
>2003-12-17 18:05:44 Using XV port 111
>2003-12-17 18:05:44 Changing from None to WatchingPreRecorded
>2003-12-17 18:05:50 prebuffering pause
>2003-12-17 18:05:53 prebuffering pause
>2003-12-17 18:05:54 prebuffering pause
>2003-12-17 18:05:56 prebuffering pause
>2003-12-17 18:05:57 prebuffering pause
>2003-12-17 18:05:59 prebuffering pause
>2003-12-17 18:06:00 prebuffering pause
>2003-12-17 18:06:03 prebuffering pause
>2003-12-17 18:06:03 RemoteFile::Read() failed in RingBuffer::safe_read()
>2003-12-17 18:06:04 Changing from WatchingPreRecorded to None
>2003-12-17 18:06:04 Changing from None to None
>
>Backend:
>
>2003-12-17 18:05:43 MainServer::HandleAnnounce Playback
>2003-12-17 18:05:43 adding: nordtv as a client (events: 0)
>2003-12-17 18:05:43 MainServer::HandleAnnounce FileTransfer
>2003-12-17 18:05:43 adding: nordtv as a remote file transfer
>2003-12-17 18:06:03 ****Aborting WriteBlock
>
>Other attempts did better but I haven't been able to run for
>more than a couple minutes without playback exiting on a false
>EOF.
>
>I also noticed that seeks are considerably slower so I did
>a test to see how long it takes to skip forward in a one hour
>remote file. The fast forward amount was set to 30 so there
>would be about 120 seek to get through the file. However, on
>four attempts I never got all the way through without a Read()
>failed in RingBuffer::safe_read(). The closest I got was 54min
>in 1:46. Without the patch it took 49 seconds to make it to
>the end of the file so seeks with the patch take more than
>twice as long.

To quote your earlier post: Bummer.

This may be a problem with the file transfer stuff, which as I indicated in
my message I wasn't sure how to test. Isaac gave me a pointer for that, so
let me look at it and hopefully that is the root of the problem when
frontend machine != backend machine.

Out of curiosity, did you try watching live tv? That code path is tested
better, I would be curious if you see the same issues.

Thanks alot for testing this for me.

-Mark