[mythtv-users] Mythbackend causing high load

[Dan Milne]

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    = 16 (on)
IO_support   =  1 (32-bit)
unmaskirq    =  1 (on)
using_dma    =  1 (on)
keepsettings =  0 (off)
readonly     =  0 (off)
readahead    = 256 (on)
geometry     = 30401/255/63, sectors = 488397168, start = 0


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} ) = 0 (Timeout)
select(45, [4 13 14 40 41 42 44], [], [], {29, 613635}) = 0 (Timeout)
select(45, [4 13 14 40 41 42 44], [], [], {29, 988476}) = 0 (Timeout)
select(45, [4 13 14 40 41 42 44], [], [], {29, 882306}) = 0 (Timeout)
select(45, [4 13 14 40 41 42 44], [], [], {29, 993259}) = 0 (Timeout)
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?


---
Dan Milne d at nmilne.com