[ltt-dev] Experiments on CPU time statistics

[Francis Giraldeau]

Hi,

I'm doing some experiments with CPU statistics, and I think that those  
computed by lttv are wrong. I did 3 tests, and for each command the  
time utility was used to get a baseline, and the command has been run  
between lttctl -C and lttctl -D to get a tight window around the test  
process.

=================================================
trace-bonnie.sh : start bonnie++ process for 10s

time statistics:
real	0m10.715s

user	0m0.420s

sys	0m6.350s


lttv statistics:

events count        : 11088588

cpu time            : 80.051904112

elapsed time        : 544.593369365

cumulative cpu time : 6.747053976

=================================================
sleep 1s : start a sleep of 1s

time statistics:
real	0m1.002s

user	0m0.000s

sys	0m0.000s


lttv statistics:
events count        : 94929


cpu time            : 7.841686487

elapsed time        : 34.566952675

cumulative cpu time : 0.036465023


=================================================
trace-burn.sh 1s * 8 process simultanés

time statistics:
real	0m1.031s

user	0m7.650s

sys	0m0.020s


lttv statistics:
events count        : 95402

cpu time            : 8.584145675

elapsed time        : 33.845893813

cumulative cpu time : 0.037255816
=================================================

I was expecting lttv enlapsed time to be close to real time, lttv  
cumulative cpu time to be greater or equal to lttv cpu time, and lttc  
cpu time to match user + sys time. Does it make sens, or maybe I'm  
getting something wrong?

Cheer,

Francis