[lttng-dev] major variations in perfomance figures

[jeremie.galarneau@efficios.com (Jérémie Galarneau)]

On Fri, Apr 3, 2015 at 10:47 AM, Wolfgang Rostek <wolfgang.rostek at gmx.de> wrote:
> Hi J?r?mie,
>
> 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.

Frequency scaling can still definitely play a role, even on a desktop machine.
Also, Core i5 chips support Turbo Boost which should be disabled to
perform benchmarks.

I'm guessing you get your time measurements from the timestamps in the
trace?

J?r?mie

>
> 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: "J?r?mie 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.
>>
>> J?r?mie
>>
>> >
>> > Wolfgang R.
>> >
>> >
>> >
>> > _______________________________________________
>> > lttng-dev mailing list
>> > lttng-dev at lists.lttng.org
>> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>>
>>
>>
>> --
>> J?r?mie Galarneau
>> EfficiOS Inc.
>> http://www.efficios.com
>>



-- 
J?r?mie Galarneau
EfficiOS Inc.
http://www.efficios.com