[mythtv] mythth 32

[Stephen Worthington]

On Fri, 8 Jul 2022 23:08:57 +0800, you wrote:

>This is not a troll but a genuine question/observation.
>
>I am biased, I do not like ubuntu because of the endless 'You shall not ... " eg dmesg eg mythtv password.
>
>After some fumbling I installed 22.04, built from scratch, using anisible, (32-fixes uptodate). I have issues ie playing while recording ... glitch back to beginning ... later ... pause of 15 secs ...
>
>I installed opensuse leap 15.4: much better but still ocassional (once-a-week) ... pause cica 15 secs ...
>
>Using the same hardware with fixes-31I've never had any glitches, ever.
>
>So it seems ubuntu 22.04 is a tad flakey (there were other minor gotchas) and it seems 32-fixes is less robust than 31-fixes.
>
>This machine runs my development VMs so it is a 4 core i7 NUC with 24G RAM and 8T flash. The only spinning rust is for backups.
>
>I do not think io is an issue
>/dev/nvme0n1p5:
> Timing cached reads:   37824 MB in  2.00 seconds = 18942.04 MB/sec
> Timing buffered disk reads: 7850 MB in  3.00 seconds = 2616.18 MB/sec
>(I know to take hdparn with a pinch)
>
>Can anybody comment on 22.04
>Can anybody comment on 32 vs 31
>
>Thanks
>James

Ubuntu versions are often a little flakey when they first come out.
That is one reason why the LTS upgrades are not recommended until the
.1 version has been released, and you have to manually override the
system to do an LTS upgrade to a .0 version.

When running any system in a VM, unless you have one that is fully set
up for real-time operation, there can be times when the main system is
busy and delays the operation of the VM.  It should not be enough to
cause problems with recordings though.  A 15 second pause is way
bigger than should ever happen.

Ubuntu packages can also have customisations of the code for things
that Ubuntu does a bit differently.  So when you compile from the
original source without the custom patches, you will not be getting
that code.  It is better to just install the Ubuntu packages from the
Mythbuntu v32-fixes repository.  But again, that should not cause 15
second pauses.

I have been running v32-fixes for quite a while now, and have not
found it to be any less (or more) reliable than v31-fixes.

The timings you posted for I/O are for reads.  NVME disks are
extremely fast always for reads.  Where they can be much slower is for
writes.  That will happen (as on any flash memory) if they run out of
erased blocks and have to erase one before they can write.  Recording
TV to an SSD causes large numbers of SSD blocks to be written to, so
it is possible that you are running out of blocks on the erased list.
Do you have the SSDs set up to do TRIM only, or have you set them to
use the discard option in fstab?  If you are doing TRIM only, then
that is likely only happening once a day at the most (unless you have
changed that), so no blocks will be being erased until TRIM is run.
Set the discard option to make the system hand back erasable blocks as
soon as they no longer form part of a file, so that the SSD can erase
them immediately.

And be aware that by recording to your SSDs, you will be seriously
increasing the wear on them.  Run smartctl on them and check the wear
values reported by SMART.

When you are playing while recording, is that playing the same
recording that is currently recording, or another different recording?
The former can be a bit glitchy if you get too close to the point
where the recording is happening.  It is best to stay a few seconds
back from that point.  The code does make an allowance for this
problem and prevents you from getting what it thinks is too close to
the point of recording, but the devs who wrote that code seem to all
be using ATSC, and I think DVB-T is just enough different that you
need to be a bit further back to avoid problems.