[lttng-dev] major variations in perfomance figures

[Wolfgang Rostek]

Hi Jérémie,

thanks for your feedback.

I've added only a loop to the end of the demo programm.

Frequence scaling I can't imagine on my dektop machine. 
It is a jump between 350ns and 800ns. In the loop below
all the events of one test run are of equal time distance, 
either slow or fast.

Wolfgang R.


https://github.com/lttng/lttng-ust/blob/master/doc/examples/demo/demo.c
...
tracepoint(ust_tests_demo, starting, 123);
for (i = 0; i < 5; i++) {
netint = htonl(i);
tracepoint(ust_tests_demo2, loop, i, netint, values,
text, strlen(text), dbl, flt);
}
tracepoint(ust_tests_demo, done, 456);
tracepoint(ust_tests_demo3, done, 42);

for (i = 0; i < 300; i++) {
if(i % 10 == 0) {
tracepoint(ust_tests_demo, done, i);         <=========
}
}

fprintf(stderr, " done.\n");
return 0;
}

> Gesendet: Freitag, 03. April 2015 um 16:22 Uhr
> Von: "Jérémie Galarneau" <jeremie.galarneau at efficios.com>
> An: "Wolfgang Rostek" <wolfgang.rostek at gmx.de>
> Cc: "lttng-dev at lists.lttng.org" <lttng-dev at lists.lttng.org>
> Betreff: Re: [lttng-dev] major variations in perfomance figures
>
> On Tue, Mar 31, 2015 at 3:46 PM, Wolfgang Rostek <wolfgang.rostek at gmx.de> wrote:
> > Hi all,
> >
> > I did a first perfomance test extending the demo example
> > by tracing 30 simple integers in a loop.
> >
> > For a similar CPU (i5 quad core 2.8GHz) I saw values
> > mentioned around 250ns in the forum.
> >
> > I've tried the test several time and could come down
> > to about 350ns. The machine was almost idle for all
> > tests.
> >
> > What makes me wonder is a large variation with frequent
> > runs giving me 750-800ns.
> >
> > Not the absolute time but the variations isn't clear
> > to me. From my understanding the caller path is more
> > or less straight to shared memory. Why do different
> > runs show more than double the time for the traces?
> 
> Good question. Can you share the benchmark's code?
> Also, make sure frequency scaling is disabled on your system; it could
> explain these kinds of variations.
> 
> Jérémie
> 
> >
> > Wolfgang R.
> >
> >
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 
> 
> 
> -- 
> Jérémie Galarneau
> EfficiOS Inc.
> http://www.efficios.com
>