[mythtv-users] High mythbackend CPU usage during DVB-T recording (Australia)
Alex Tomlins
alex at tomlins.org.uk
Sun Jul 14 13:02:31 UTC 2013
On 14/07/13 11:57, Christian Hack wrote:
>
> Hi everyone
>
> Having some issues with my latest incarnation of MythTV.
>
> It’s mythbuntu based from 12.04 and updated to the latest everything.
> Mythbackend reports as “mythbackend version: fixes/0.25
> [v0.25.3-48-g3a1eff8] www.mythtv.org <http://www.mythtv.org>”
>
> CPU is an i3-2100 on an ASRock B75-PRO3-M motherboard, 3GB RAM, 3TB
> main drive and a couple of other smaller ones. Playback is VDPAU which
> works OK.
>
> hdparm –t reports speeds of 60-70MByte/sec no problem on all drives
> and only 4-5MB/sec when recording as expected. There seems to be no
> actual issue with recordings. There are no corruptions or dropouts
> ever that I notice.
>
> Tuners are two dual tuner “USB Lifeview TV Walker Twin” devices for a
> total of 4 DVB-T tuners. I have 4 virtual tuners on each although
> rarely do they ever get exercised to the full extent. Helpful for
> overlapping recordings though.
>
> My problem is that when a recording is running I’m seeing quite high
> CPU usage from mythbackend. A HD show (1440x1080) will take 60-80% CPU
> per recording. When a couple of recordings are going I see something
> like the top output below (2 x HD and 1 x SD recordings) with a load
> average to match. DVB-T recordings really shouldn’t need much/any CPU.
> Load average occasionally even gets up to 8-10 or more.
>
> top - 20:46:06 up 1 day, 8:55, 3 users, load average: 5.29, 5.88, 6.49
>
> Tasks: 211 total, 2 running, 208 sleeping, 1 stopped, 0 zombie
>
> Cpu(s): 20.4%us, 29.0%sy, 0.1%ni, 45.4%id, 5.1%wa, 0.0%hi, 0.0%si,
> 0.0%st
>
> Mem: 3023632k total, 2953156k used, 70476k free, 12280k buffers
>
> Swap: 9765884k total, 447804k used, 9318080k free, 1418564k cached
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
>
> 4197 mythtv 20 0 2927m 121m 6040 S 202 4.1 1028:10 mythbackend
>
> 8672 mythtvus 20 0 3007m 247m 30m S 4 8.4 57:35.85 mythfrontend.re
>
> 1627 root 20 0 188m 51m 23m S 1 1.7 4:59.26 Xorg
>
> 595 root 20 0 0 0 0 S 0 0.0 0:20.11 jbd2/sda3-8
>
> 1419 mysql 20 0 2434m 152m 4212 S 0 5.2 75:42.51 mysqld
>
> 1462 root 20 0 32908 604 504 S 0 0.0 3:47.02 lircd
>
> 2705 nobody 20 0 16972 704 636 S 0 0.0 5:21.88 LCDd
>
> This in turn really slows the whole system down which is a problem
> since it’s an all in one machine. Often it will drop out with
> “irrecoverable recorder error” back to the recordings screen. The
> recording doesn’t seem at affected though and I just start it again
> and it works. 1000 minutes over 32 hours is a fair bit of CPU time
> just for recordings. Doing something like moving a file from one disk
> to another seems to make it even worse (but I get a get 60-70
> MByte/sec transfer speeds)
>
> I only have a 1 instance of mythcommflag running at once but even
> killing that one makes no difference. It’s a separate process anyway.
>
> This didn’t happen previously (was using Mythdora 12.25) on the same
> tuners (same CPU but different motherboard).
>
> Otherwise it works quite well. Is this CPU usage likely to be MythTV
> building the recordedseek table for the recordings that are running?
> That’s about all I can think of. Is it normal now?
>
> Sorry about the length - tried to include as much detail as I can. I
> don’t see much that is helpful in any logs.
>
> Any ideas? Is this just “normal”? With a few recordings it’s a bit
> painful to use particularly when it keeps dropping out of playback.
> The machine is not a powerhouse but should be easily capable of what
> I’m doing.
>
That does sound a little high to me, but it could just be due to the
fact that USB relies on the CPU for a lot (hence it's cheap).
As another data point for comparison, my system is sitting at around
16-19% while recording 2 SD DVB-T programmes from a Nova T-500. This
with a Celeron E3400 CPU, and writing to a mirrored pair of SATA drives.
thanks,
Alex
P.S. the Nova T-500 is actually a USB tuner, even though it looks like a
PCI card - http://www.linuxtv.org/wiki/index.php/Hauppauge_WinTV-NOVA-T-500
--
Alex Tomlins
Email/Jabber: alex at tomlins.org.uk
There are two kinds of people in the world: those who finish what they started
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