[mythtv-users] Mythbackend causing high load

Ryan Steffes rbsteffes at gmail.com
Tue Jun 13 19:06:09 UTC 2006


On 6/11/06, Dan Milne <d at nmilne.com> wrote:
>
> Hi Guys,
>     I have a problem with Mythtv version 0.19_p9163-r1 on Gentoo
> where load suddenly spikes up to the 10 - 25  range. I'm running both
> back and front end on the same box and it make it unusable.  Top
> tells me the load is between 10 - 25 with 0.0 % idle time. There's
> some 13G of disk free ( 95% used ).
>
> CPU is  AMD Athlon(tm) 64 Processor 3000+  with around 512MB of RAM.
> I've got 3 Technisat SkyStar2 DVB card s which work fine.  I'm only
> recording digital content.
>
> Hdparm reports the following for the drive containing the mythtv
> recordings:
>
> mythbox ~ # hdparm /dev/hdb
> /dev/hdb:
> multcount    > IO_support   > unmaskirq    > using_dma    > keepsettings > readonly     > readahead    > geometry     >
>
> When I strace the mythbackend process, some of the time, I get this:
>
> mythbox ~ # strace -p 9373
> Process 9373 attached - interrupt to quit
> select(45, [4 13 14 40 41 42 44], [], [], {15, 456000} ) > select(45, [4 13 14 40 41 42 44], [], [], {29, 613635}) > select(45, [4 13 14 40 41 42 44], [], [], {29, 988476}) > select(45, [4 13 14 40 41 42 44], [], [], {29, 882306}) > select(45, [4 13 14 40 41 42 44], [], [], {29, 993259}) > select(45, [4 13 14 40 41 42 44], [], [], {29, 848225}
>
>
> In the mythbackend log file I see this:
> 2006-06-11 22:50:48.325 TFW, Error: Write() -- IOBOUND end
> 2006-06-11 22:50:48.329 TFW, Error: Write() -- IOBOUND begin cnt
> (9400) free(6627)
> 2006-06-11 22:50:50.113 TFW, Error: Write() -- IOBOUND end
> 2006-06-11 22:50:50.113 TFW, Error: Write() -- IOBOUND end
> 2006-06-11 22:50:50.117 TFW, Error: Write() -- IOBOUND begin cnt
> (9400) free(7699)
> 2006-06-11 22:50:50.120 TFW, Error: Write() -- IOBOUND begin cnt
> (9400) free(1683)
> 2006-06-11 22:50:50.133 TFW, Error: Write() -- IOBOUND end
> 2006-06-11 22:50:50.134 DVBRec(1): PID 0x301 discontinuity detected
> 2006-06-11 22:50:50.135 DVBRec(1): PID 0x302 discontinuity detected
> 2006-06-11 22:50:50.135 DVBRec(1): PID 0x304 discontinuity detected
> 2006-06-11 22:50:50.139 TFW, Error: Write() -- IOBOUND begin cnt
> (9400) free(2259)
> 2006-06-11 22:50:51.695 TFW, Error: Write() -- IOBOUND end
> 2006-06-11 22:50:51.695 TFW, Error: Write() -- IOBOUND end
> 2006-06-11 22:50:51.698 DVBRec(0): PID 0x200 discontinuity detected
> 2006-06-11 22:50:51.701 DVBRec(2): PID 0x2d0 discontinuity detected
> 2006-06-11 22:50:51.701 DVBRec(0): PID 0x28b discontinuity detected
> 2006-06-11 22:50:51.702 DVBRec(2): PID 0x2d1 discontinuity detected
> 2006-06-11 22:50:51.703 DVBRec(0): PID 0x28a discontinuity detected
>
>
> And this:
> 2006-06-11 23:02:06.331 DevRdB(0) Error: Driver buffers overflowed
> 2006-06-11 23:02:06.342 TFW, Error: Write() -- IOBOUND end
> 2006-06-11 23:02:06.342 TFW, Error: Write() -- IOBOUND end
>
>
> Does anyone else experience these types of loads? Obviously the
> IOBOUND stuff is bad news - I can't see why it would be so IO bound
> tho - just recording a couple of channels shouldn't cause that right?



I've been looking for an answer to this, it seems to be happening to more
and more people.  Typically, the thread will go like this:

Someone asking about DMA settings, someone asking about what other tasks are
running, someone possibly suggesting a driver upgrade.  There's also the
occasional mysql optimization suggestion.

Then it fades away without ever really being resolved.

Personally, I disabled mythtranscode on the backend machine, even though
there is no way my IO should be hitting bandwidth limits without there being
another real problem on my machine, and I can load up the hard drives
otherwise without seeing any other problems at all.

There definitely seems to be a problem, but I don't know how to go about
tracking it down.  Like I said, for me, pushing the transcoding off to a
slave seems to have mostly fixed it, even though it's the mythbackend
process that's acting up.

Ryan
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