[mythtv-users] Repeating audio on SMP machine

Kane Tse kanetse at hotmail.com
Mon Dec 6 19:38:41 UTC 2004

>Try forcing the capture card and audio capture IRQ processing onto one
>CPU. It could be that the process is being migrated between CPUs and
>the driver is not completely SMP safe.

I read up on the smp_affinity file and made the modifications, but 
ultimately, it didn't help.  I made the following observations:

1) When I did a 'cat /proc/irq/17/smp_affinity', I got 00000001 suggesting 
the IRQ was redirected to CPU0.  But when I did:

cd /proc/irq/17
cat smp_affinity

I got 00000002.  Which is really strange, since they should be the same file 
right?  Also, this also suggested that input is already handled by one CPU, 
namely CPU0.

2)  When I did an lspci -v | grep 17:, I noticed CPU0 was handling almost 
all the processing for that card, so did an echo 2 > 
/proc/irq/17/smp_affinity to redirect IRQ processing onto CPU1.  Performing 
a 'cat /proc/irq/17/smp_affinity' showed 00000002, which suggested that IRQ 
processing was being handled by CPU1.   This was confirmed by lspci -v | 
grep 17:.  But after a few minutes, 'cat /proc/irq/17/smp_affinity' reverted 
back to 00000001... for no reason, and the problems didn't go away (although 
i couldn't tell if this was before or after the reversion back to 00000001.

What's up with that?  Why did it revert back?

Anyway, it seems to me that CPU0 was already directed to process input from 
IRQ17, so maybe that wasn't my problem.  But tonight when I get home I am 
going to clean-install Fedora Core 3 on that machine and see if things 
improve or not.

Thanks for your help though.  And let me know if you have any other ideas.

Is anyone else out there running a bt8x8 and btaudio on an SMP setup?  Which 
OS are you using?  Any problems?

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