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

Christian Hack christian at hack.id.au
Thu Jul 18 02:01:17 UTC 2013


On 16 July 2013 21:56, Anthony Giggins <seven at seven.dorksville.net> wrote:

>
>
>  On 16 July 2013 18:38, Christian Hack <christian at hack.id.au> wrote:
>
>>
>>  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
>>
>>
>> Sounds tuner related, I'm running a HDhomerun also in AU also on
> mythbuntu 12.04 (0.26-fixes) and I'm not seeing these issues, the other
> thing you might want to confirm is if your mysql database is running on
> ext4 as there are optimisations required there or reinstall with ext3
> instead.
>
> Cheers,
>
> Anthony
>
>
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>
I'm quite sure the same tuners on a different motherboard didn't do this
with 0.25 on Mythdora. If I play directly using mplayer or similar that
would rule out the hardware, kernel drivers, USB etc wouldn't it?

The file system is ext4 so I will investigate that wrt mysql. Thanks.
Certainly it lags a bit when starting to *play* a recording. It seems to
hit the DB for recordedseek for that program. If you exit and play the same
again, it starts much faster so I presume it's cached then. At one point I
had changed it over to InnoDB and that made quite a difference on that
table.

Christian
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