[mythtv-users] Backend going to 100% CPU

[Michael T. Dean]

On 03/31/2008 11:04 AM, Steven Adeff wrote:
> On Sat, Mar 29, 2008 at 8:34 PM, Bob Cottingham <bobnvic at gmail.com> wrote:
>   
>> Since upgrading to .21-fixes my backend has going to 100% CPU.  I
>>  noticed this once when I ran mythweb, however I haven't used mythweb
>>  since and it has happened again repeatedly. What do I need to include
>>  if I submit a ticket? I assume that a backtrace won't show anything
>>  since it doesn't crash.
>>     
>
> first, is the version of MythWeb your running the same as the version
> of mythbackend your running?
> if so, try running mythbackend with the --noupnp option and see if that helps.

Also, there have been reports of this happening because of problems with
the XML-based preview request mechanism in the backend that's used by
MythWeb.  For a while, it happened on almost every machine.  Then, the
problem just "disappeared" for most, though no one fixed it (it's likely
a race condition for which the timing changed just enough because of
unrelated modifications to Myth to prevent the problem on some
machines).  However, one person--the author of MythWeb, Chris
Petersen--has actually seen it since.  You may be the second person.  If
it's 100% reproducible by just requesting XML previews repeatedly, you are.

If you want to find out, feel free to run the attached (hack of a)
script (when the backend isn't running at 100%) to see if it causes the
CPU to max out (make an empty temp directory from which to run it as it
will drop a bunch of previews in the dir).  If so, you might be able to
work around the problem by changing the timing on your backend machine a
bit (i.e. by underclocking it a little or something).  Note that this
script is meant only as a diagnostic tool and is not developed to be
generally useful.  It has some stuff hardcoded, so you may need to
modify it a bit.

Mike
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