[ltt-dev] Experiments on CPU time statistics

[Mathieu Desnoyers]

* Francis Giraldeau (Francis.Giraldeau at USherbrooke.ca) wrote:
> 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

cpu time should be good. How many cores does you machine have ? 8 ?

>
> elapsed time        : 544.593369365

Elapsed time is the total of the per-thread elapsed time I think (it's
really been a while since I played with this code though). It would make
sense if you have 54 threads in your system.

I don't have entire confidence that the elapsed time is correct.

>
> cumulative cpu time : 6.747053976

cumulative cpu time is known to be wrong.

Thanks,

Mathieu

>
> =================================================
> 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
>
>
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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com