[mythtv-users] MythTV and Satellite

Rob Kaufman rgkaufman at gmail.com
Tue Mar 21 22:51:37 UTC 2006


Dan,
  The section of the kernel they are configuring is all about the
interrupt scheduler (the part of the kernel which controls which
processes get interrupted and how often.  Therefor different hardware
/ kernel / lirc combinations can have very different success rates. 
The following things will effect how often a process gets interrupted:
* Hardware - Are you CPU bound?  Memory bound?
* Other process - Is there another process that is interrupting your
lirc call?  Does that process take a long time to complete, or are
there many other processes that get run?  This is where decreasing the
nice value of lircd comes in to play, a process can't interrupt one
that is "less nice" than it.
* Kernel preemption / latency - Does the big kernel loop grab your
processor and hold it hostage for a little while?  Does your lircd
process get interrupted all the time because your switching context
too rapidly? Not rapidly enough?

The 'nice' value of the process is the easiest to fix, but if it is
the kernel that is interrupting your send than this solution won't
help.

-Rob
On 2/8/06, Dan Wilga <dwilga at mtholyoke.edu> wrote:
> At 9:23 AM -0700 2/7/06, James Dastrup wrote:
> >Maybe it does have something to do
> >with settings in that particular section of the kernel configuration
> >(Processort Type and Features), or we could both be wrong and maybe
> >it only has to do with a good lircd config and channelchange script.
>
> It's definitely got nothing to do with the config or channel changing
> script, as I changed neither.
>
> After lots of testing, I had come to the conclusion that the reason
> for the problem in the first place was that lirc was getting
> interrupted while toggling the serial port line at what is an
> unusually high rate (56 KHz.)
>
> So either the newer lirc I'm now using is more tolerant of
> interrupts, or the newer kernel no longer interrupts when it should
> not (or both.)
> --
> Dan Wilga                                         dwilga at mtholyoke.edu
> Web Administrator                             http://www.mtholyoke.edu
> Mount Holyoke College                                Tel: 413-538-3027
> South Hadley, MA  01075            "Who left the cake out in the rain?"
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