[mythtv-users] High mythbackend CPU usage during DVB-T recording (Australia)

[Christian Hack]

On 16 July 2013 06:12, HP-mini <blm-ubunet at slingshot.co.nz> wrote:

> On Mon, 2013-07-15 at 14:20 +1000, Christian Hack wrote:
> >
> >
> > On 15 July 2013 08:36, Kenni Lund <kenni at kelu.dk> wrote:
> >
> >         Den 15/07/2013 00.28 skrev "Kenni Lund" <kenni at kelu.dk>:
> >
> >         >
> >         > Also, do you use get your EPG from EIT? If not, you should
> >         be able to save some CPU cycles by disabling EIT.
> >         >
> >         > FYI, the upcoming MythTV 0.27 contains multiple
> >         optimizations which should lower the CPU utilization when
> >         recording (see for example ticket #12250, #11252 or #11255)
> >         Sorry, that should have been #11250, not #12250.
> >
> >         Best regards
> >         Kenni
> >
> > Gave 0.26 a whirl last night and after fighting a number of issues
> > which were a pain (mysql timezone issue, mythweb broken,
> > mythtv-database upgrade failed, password issue in config.xml), I have
> > 0.26 running. Unfortunately that also seems to have mostly broken the
> > PiP which had previously worked fairly well in 0.25 with VDPAU :( .
> > Just when I needed it for Tour de France and the Ashes...
> >
> > Anyway, with 2 HD recordings that I had running CPU usage dropped from
> > what would normally be around 130%-140%-150% to around 90%. Still
> > fairly high in my opinion but definitely improved noticeably.
> >
> > EPG comes from a scraper. EIT is off on all tuners and also even on
> > the channels themselves and I've never used it here since it's (well
> > was) a bit rubbish.
>
> Old *buntus are likely to cause HDD partition alignment issues (on big
> disks) that could cost ~20% disk throughput.
>
>
Brand new install of 12.04. Even then I get 50-60MByte/sec throughput when
copying from disk to disk. So recording a few MByte/sec should be no issue.
It shouldn't cause high CPU usage in the backend. Maybe IO waiting.


> Is the high CPU use caused by one or more CPU cores stuck at 100%?
> Are you auto-running mythcommflagging/transcoding?


No. As mentioned mythcommflagging is set to only one thread that is
separate to the the mythbackend's CPU usage and killing it makes no
difference. No transcoding but again that would be a different process.


> Are any high CPU usage tasks named mythlogserver? there could be
> several..
> This seems to go rogue if mythbackend logging options are not right.
> Do the BE & mythlogserver logs & their contents appear okay?
> This high CPU usage is with no FE playback right ?
>
>
No mythlogserver processes going crazy - I've not seent that issue. Again
this wouldn't explain mythbackend using a lot of CPU to record. The high
CPU usage is with recording only with or without mythfrontend doing
anything. The 4% usage in the original post is typical and that was playing
a HD stream. VDPAU is working well for me with very little CPU required.


> Check your mythtv-backend upstart job script against the mythtv wiki
> page.
> AFAIK mythbuntu has a FE wrapper script that re-spawns the FE if it
> crashes.
>
>
Check what exactly? I'm using the standard mythbuntu setup. I don't really
see how or why this could be an issue. Yes mythbuntu respawns the frontend.


> I don't recall seeing your graphics h/w except for iCPU/IGP.
> VDPAU video decode/playback is only possible on nVidia GPU (all recent)
> & some (& only some) AMD when using FOSS radeon driver.
> VA-API is viable option on some intel GPU & the latest haswell could
> eventually be a match for VDPAU.
>
>
nVidia GT440 running VDPAU very successfully and as noted working fine.
Again, not a mythbackend issue.

Christian
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