Execution lags

Ancoron Luciferis ancoron at chaoslayer.de
Sat Mar 13 12:32:55 GMT 2010


Hi *,

I really don't want to disturb your hard work but I've got a problem 
that I'm unable to find a reason for.

I'm currently running Kubuntu Lucid with latest updates on an AMD Phenom 
II X4 machine. The problem is, that execution of anything lags sometimes 
until I press some key or move the mouse.

For this to messure I used a simple command line:

while [ 0 ]; do oldtime=$time; time=`date +'%s.%N'`; echo "($time - 
$oldtime - 1) * 1000" | bc -l | xargs printf "[$time] missed %1.0f 
ms\n"; sleep 1; done | tee ticks.log


The output of that looks like this:

[1268440070.490933942] missed 1268440071491 ms
[1268440071.562506937] missed 72 ms
[1268440072.580239127] missed 18 ms
[1268440073.597819427] missed 18 ms
[1268440074.615416926] missed 18 ms
[1268440075.633107479] missed 18 ms
[1268440077.765155286] missed 1132 ms
[1268440078.778187875] missed 13 ms
[1268440079.792391115] missed 14 ms
[1268440080.806246041] missed 14 ms
[1268440081.818535399] missed 12 ms
[1268440082.834927532] missed 16 ms
[1268440083.849656171] missed 15 ms
[1268440084.865000558] missed 15 ms
[1268440085.882215112] missed 17 ms
[1268440086.898824440] missed 17 ms
[1268440087.917051832] missed 18 ms
[1268440088.933482288] missed 16 ms
[1268440089.949114926] missed 16 ms
[1268440090.966478632] missed 17 ms
[1268440091.983695874] missed 17 ms
[1268440093.000970062] missed 17 ms
[1268440094.017714305] missed 17 ms
[1268440111.553100689] missed 16535 ms
[1268440112.565352587] missed 12 ms
[1268440113.585565660] missed 20 ms
[1268440114.598418830] missed 13 ms
[1268440115.615446402] missed 17 ms

When I ran that command nothing CPU intensive was running so the 
differences should be within a few milleseconds but as you can see 
sometimes they are not. During those longer "pauses" I can press a key 
to stop the pause and to continue running.

These lags affect all processes, ot only the command line. The whole 
screen freezes during that "pause" time and this even happens e.g. when 
running some package update or even at shutdown.

I carefully checked all the logs available on my system to get some kind 
of hint but without success.

I let that command run over night to see how big those lags go usually 
during idle time and this is what I got (top ten):

$ sed '1,1d' ticks.log | awk '{print $3 " ms " $1}' | sort -rn | head 
-10 | awk '{print $3 " missed " $1 " ms"}'
[1268441221.483105541] missed 58989 ms
[1268442781.361738141] missed 56980 ms
[1268452136.116237759] missed 54297 ms
[1268457480.726283135] missed 51632 ms
[1268468280.295310837] missed 50872 ms
[1268442301.336665143] missed 49843 ms
[1268476556.072677119] missed 49462 ms
[1268460301.451315487] missed 48832 ms
[1268457288.692267086] missed 47441 ms
[1268477333.834187845] missed 47371 ms

So up to one minute the system freezes without actually freezing. When 
there is some CPU usage like watching a HD video or doing some 3D 
rendering inside a VM those lags don't occur.

Please help me here sorting out the core reason for this. I don't know 
where to start looking.

Ancoron.




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