[mythtv] mythcommflag control suggestion

Robert Johnston anaerin at gmail.com
Mon Apr 3 03:28:51 UTC 2006


On 4/2/06, Ambrose Kofi Laing <aklaing at gmail.com> wrote:
> Hi Everyone,
>
> first post here.  I have a problem with mythcommflag.  Somehow when it runs,
> encoding (by PVR-350) seems to include artifacts.  Playback has lots lof
> little split-second
> freezes.  There is no problem at all if I switch things off so that
> mythcommflag does
> not run while recording.  Its an underpowered PC I know.
>
> I know mythcommflag runs nice (17), but that seems to still not be good
> enough for
> not interfering with other processes.
>
> I also know it is possible to set up a window of time during which
> mythcommflag can run,
> and no jobs will be initiated outside this window.   That works best if
> there is a window during
> which I never want to record any shows.  However some of the shows I record
> are sitcom
> reruns that run at all sorts of odd hours.  If I could keep these windows
> disjoint from the
> recording sessions, that would be great, but the interface is obviously
> designed so that you
> set the mythcommflag window once and leave it alone.
>
> So my suggestion is that if possible mythcommflag should be designed to be
> able to dynamically adapt
> its operation to run outside the recording and playback sessions.  That is,
> when any recording
> or playback is happening, mythcommflag will not run, and when nothing is
> happening, we don't need
> to tell mythcommflag to run, it just kicks into gear on noticing the silence
> and does what it has to do.
> The goal is to have mythcommflag automatically know what the recording
> schedules are and what the
> users' viewing activity is, and know how to stay off the radar in those
> times.  If this can be arranged,
> then mythcommflag can run with no high nice setting, just barge through the
> job and be done with it.
>
> One way I was thinking of doing this (preferably without touching any source
> code for right now),
> is to misuse the commands for turning the machine off and on when nothing is
> happening.  It is intended
> for shutting down and waking up, but can we use those hooks to instead
> enable and disable
> mythcommflag?  That way, whenever the machine thinks it is safe to go to
> sleep because no recording
> or viewing is happening, it will instead permit mythcommflag to run.  And
> when it thinks it is time to come
> back on, it will instead disable mythcommflag.
>
> Any reactions welcome -- either on how to get this implemented as a standard
> feature, or how I
> can configure my own installation to have that behavior with the minimum of
> work.

Personally, I think having the commflag nice(17)'d already achieves
this. It's set below everything that could possibly be causing
artifacts like this (Including Mythbackend and IVTV). However, if your
HDD is running in a PIO mode (Without DMA), or if your FS is extremely
fragmented, it could be that the FileSystem is blocking as it changes
from a write of the current recording to a read of the commflagging
file. Check that DMA is enabled, and that your FS is running properly.
In thoery there should be more than enough bandwidth on even the
oldest IDE hard-drives to cope.

If your system is already DMA'd, then chances are you're running a
very slow system, and perhaps commflagging should be completely
disabled. You say the system is "Underpowered"... just how
underpowered are we talking here?
--
Robert "Anaerin" Johnston


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