[mythtv-users] scheduler confusion

Michael T. Dean mtdean at thirdcontact.com
Fri Sep 5 15:59:39 UTC 2014


On 09/05/2014 11:15 AM, Mark Perkins wrote:
> From: Michael T. Dean
>> On 09/05/2014 08:25 AM, Michael T. Dean wrote:
>>> On 09/05/2014 07:52 AM, Mark Perkins wrote:
>>>> To be honest I don't think the ordering is causing your problem, but
>>>> the recommendation is that if all the tuners are equally functional
>>>> then that should be reflected in the order priority.
>>> Though not all having the same value.  If you have 4 physical capture
>>> devices, all equally functional and equivalent to one another, you
>>> should set them up as having schedule orders of 1, 2, 3, and 4.  Then,
>>> you would likely choose Live TV order of 4, 3, 2, 1 to ensure you take
>>> the least-likely-to-be-chosen-for-recordings device first when you
>>> enter Live TV (so it's also the least likely to be already locked to a
>>> mux).
>> Oh, and BTW, this is exactly how MythTV will configure your system by
>> default.  If it's not already this way, I highly recommend you "Delete all
>> capture cards" (not "Delete all capture cards on<hostname>") and
>> re-create them to ensure they're fixed properly so you don't:
>>> Choosing exactly the same schedule order value for the different
>>> physical devices may break multirec placement efficiency.
>> break multirec.
> Mike, this appears to be the opposite answer to what you gave me when I went
> through this exact issue earlier this year. In particular you said:
>
> MythTV, in absence of instruction to do otherwise, will always schedule
> recordings on the first-available input that can be used for that
> recording. So, if it's doing otherwise, you've told it to do otherwise.

Yes, so when it puts a recording from mux 1 on physical device 1/virtual 
tuner 1 and a recording from mux 2 on physical device 2/virtual tuner 4 
and it tries to place another recording from mux 1, it will do so on 
physical device 1/virtual tuner 2, which means it shares the same 
physical tuner and maximized multirec efficiency.

The only time this is "broken" is when you have a so many concurrent 
recordings on a given mux that at least one of them spills over to 
another physical device (say you now have devices 1 and 3 recording from 
mux 1) and the recording on the "later" (= higher scheduling order, in 
this example device 3) device has a longer run time than all of the 
recordings on the earlier device (device 1).  At the point the final 
recording on device 1 finishes, device 3 is being used for mux 1, but if 
a new recording from mux 1 starts when device 1 (and 2) is not being 
used for recording from other mux'es, it will start the new recording on 
device 1, so you'll still have devices 1 and 3 used for the same mux 
until the recording on device 3 finishes.  In other words, you'll need 
both a spill over (more concurrent recordings on a given mux than 
virtual tuners on the physical device) /and/ the latest-ending recording 
must be placed on the higher-schedule-order device /and/ a new recording 
from the same mux must start before that (latest-ending) recording on 
the higher-schedule-order device ends /and/ at least one 
lower-schedule-order devices must be 
unoccupied/not-in-use-for-a-recording-on-a-different-mux at the time.

This is enough of a corner case that it's really not worth trying to 
"fix"--especially as there are nearly as many ways that assigning the 
new recording to the later-schedule-order device will break other future 
recordings as there are ways that the above issue will actually break 
recordings (where "break," here, tends to mean "cause conflicts").

> There was another thread where you detailed that unless tuners otherwise had
> shortcomings or limitations they should have the same priority, but too
> tired to try and find it at the moment.

Input (tuner/card) Priority is /very/ different from Schedule Order and 
Live TV Order.  Order should increment for each physical device, in the 
order in which you want devices to be used (lowest used first) and 
applies to both recordings (Schedule Order) and Live TV (Live TV 
Order).  Priority affects whether a recording (and only a recording--it 
has no effect on Live TV) from that input is better or worse than a 
recording from another input--and with priority, higher is "more 
preferred" (meaning higher is generally used first).  So, they have 
completely different purposes, and their values have opposite effects.  
And, input priority will actually break multirec placement 
efficiency--therefore, all inputs should have the same priority unless 
they have shortcomings or other limitations compared to other inputs.

Unfortunately, confusing Priority and Order is actually a /very/ common 
mistake among users.  We (I?) just haven't been emphasizing the 
difference enough since Order was introduced.  People are still thinking 
as they did in the days of Anarchy--when there was only Priority (the 
time before David Engel introduced Order to MythTV :).  Please help 
spread the word since I've been shirking my duties on list.

Mike


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