[mythtv-users] Re: Mythbackend dies while using two tuner cards

William Powers wepprop at sbcglobal.net
Sat Nov 22 19:36:07 EST 2003


 > mythtvbackend is dying on me when I try to use 2 tuner
 > cards simultaneously. I've tried spreading my
 > peripherals across the interrupts more thinly, and
 > made sure that the HDD DMA was turned on. One card
 > operation is great.
 > Two operation card crashes the backend after about 4-5
 > seconds

Until recently, I was running two tuner cards - an ivtv card as the first 
card and a bttv card as the second (I bought a second ivtv because I 
couldn't get the brightness balanced across the two cards).  I used to get 
backend crashes whenever the bttv card was recording and something tried to 
query mysql, such as the start of a recording on the ivtv card or a mythweb 
request.

After I finally noticed the pattern, I theorized that mysql was getting 
swapped out to virtual memory while software encoding was going on and 
didn't have sufficient priority to get swapped back in in time to respond 
to backend requests.  As an experiment, I tried starting mysql at nice 
-5.  Since then, I haven't had a single backend crash.  Obviously, that 
could bring the system to its knees if mysql is being used for other 
applications with large or frequent queries.  But it seems to work just 
fine on my dedicated myth box.






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