[mythtv-users] Problems in load-balancing commflagging

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Tue Dec 6 17:56:39 EST 2005

In 1.18.1:

I'm trying to figure out if I can load-balance commflagging.  I've got
an MBE/SBE setup with 5 250's in the BE and one 350 in the SBE/FE.
Commflagging is set to begin immediately upon episode start.  I'd like
to run commflagging as soon as possible, in parallel as much as
possible, since it appears that I can easily run 5-6 jobs on even one
of my hosts without really saturating it.  (Well, 5 commflaggers
saturate the CPU, but not the disk, and I see no skipping in the
recordings being made while this happens.)

However, I've got some problems:

(a) The setup page that deals with running jobs tops out at 5, e.g., I
    can't tell myth to schedule more than 5 jobs in parallel because
    the control just won't go any higher.  Why's it got this limit?
    (The jobs also started 1 minute apart, so doing 5-minute test
    recordings meand that the 5th job didn't evne start until the
    recordings were over, so I set the time to check between jobs
    from 60 seconds down to 10.  I'd be happy if that could be set
    down to 1, if it didn't cause Myth to thrash, or, even better,
    if it was smart enough to start -all eligible jobs at once- in
    each sweep---then I could leave it at the default 60s, but all
    commflagging jobs would be started simultaneously, one per
    simultaneous recording.)
(b) Possibly because of (a), if I do a test recording of 6 things
    simultaneously, commflagging only happens on 5 of them at once.
    The 6th waits until the others are done, and then runs.  They
    all run on the MBE, even though I don't have "run jobs only on
    original recording host" set, but OTOH, there's that cap of 5
    jobs total, so would I ever see that sixth job on the SBE?

What I'd -like- to see happen is for all 6 jobs to run at once.  Even
if 5 of them run on the MBE and one runs on the SBE, that's actually
okay with me, because I can probably soak up the remaining CPU on the
SBE doing transcoding from MPEG2 to MPEG4, but to do this requires
that I have a lot of jobs running.  (I don't know if transcoding will
count against the 5-job limit I see or not, since I haven't yet
managed to get transcoding to run at all; see previous message.)

An even cleverer thing (but which I wouldn't be surprised can't happen
in the current Myth architecture) would be to load-balance the commflagging,
so that (if I'm recording with 6 tuners), 3 of them happen on the MBE,
and 3 happen on the SBE.  Myth would have to be reasonably intelligent
in its job-scheduling for this to work, though.  And it still might
make sense to try to push as many of them on the MBE as possible,
since commflagging can't happen -faster- than real-time anyway for
recordings in progress, and this would leave the SBE free to be the
transcoding engine.


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