[mythtv-users] High load, low CPU usage

Steve Hill steve at nexusuk.org
Fri Jul 11 22:33:27 EDT 2003


On Fri, 11 Jul 2003, Ray Olszewski wrote:

> 1. What is CPU utilization when "playing at the same time (e.g. LiveTV)"? 
> You left that detail out, and I'd like to know whether or not there is 
> really "plenty of free CPU time" in that setting.

There's around 50% free CPU time in liveTV mode, even though the load 
average is sky high.

> 2. Are you certain that you are using the recording profile you describe 
> above for *both* the default and the live-TV profiles?

Yes, I just doublechecked the settings and they are both identical.  
If the backend is already doing a scheduled recording then the problem 
still happens if I start up a playback on the frontend at the same time 
(i.e. not livetv).

> 3. I'm puzzled by your saying that Myth "isn't hitting the disk much 
> anyway". It has to be writing to the buffer, and I think Isaac said Myth 
> was set to force a sync every second (but check the list archive to be sure 
> of this). But a DMA problem would show up in recording mode, not just in 
> "live" TV mode, so that probably isn't it.

I just looked at the disk light - a brief flash about once a second.  What 
I meant was that it wasn't really thrashing the disk.

> 5. The extremely high load average suggests that the live-TV choice leads 
> to some process that blocks. Offhand I cannot see what it might be; listing 
> (say) the top dozen of so processes in a "top" listing might suggest 
> something, though.

  9:31pm  up 12 days, 12:34,  5 users,  load average: 2.37, 0.89, 0.67
150 processes: 147 sleeping, 3 running, 0 zombie, 0 stopped
CPU states: 18.2% user,  2.5% system,  0.0% nice, 79.1% idle
Mem:   255492K av,  252024K used,    3468K free,   0K shrd,  5008K buff
Swap:  530136K av,  146180K used,  383956K free             83944K cached

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME COMMAND
 4026 root      -1 -20 70116  53M  5496 S <  13.5 21.2   0:21 mythbackend
32453 root      11   0  334M  39M 12828 R     2.9 15.7   7:59 X
 8470 steve      9   0 42528  41M 21208 S     2.5 16.6   0:08 mythfrontend
 8701 root      10   0  1148 1148   852 R     0.5  0.4   0:00 top

There's basically nothing using any CPU under those.

> 6. A real longshot here -- is it possible that the bttv and the sound card 
> are using the same IRQ? Or that you have a sound card that has trouble with 
> full-duplex, something that would show up only when simultaneously 
> recording and playing (e.g., "live'" TV)? This is pretty wild guessing, though.

The machine has 2 soundcards in - a Soundblaster Live (used for the input) 
and a VIA82Cxxx on the motherboard used for the output.  I've tried 
switching the output to the SBLive, which didn't affect the problem at 
all.
Looking at the IRQ list, both soundcards are on IRQ 10 and the TV card and 
video card are both on IRQ11, so this could be the problem (I will reboot 
in a bit and see if I can convince the bios to move them all onto 
different IRQs).

> 7. Some miscellaneous items: How much RAM is in the system? What gbuffers 
> setting do you use with the bttv driver? What sound modules (OSS? ALSA?) ar 
> you using?

256MB of RAM (possibly not quite enough, but according to top the kernel 
is using 100MB of it as cache).
What's the gbuffers setting?  I've not come across that before.
And I'm using the stock EMU10K drivers (I think that's OSS).

Thanks for your help

-- 

 - Steve                                             http://www.nexusuk.org/

"..Learning that we're only immortal for a limited time.." - Dreamline, Rush
        *** Presented in DoubleVision (Where Drunk) - Futurama ***




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