On Fri, Apr 3, 2015 at 10:47 AM, Wolfgang Rostek <[email protected]> wrote: > 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.
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? Jérémie > > 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" <[email protected]> >> An: "Wolfgang Rostek" <[email protected]> >> Cc: "[email protected]" <[email protected]> >> Betreff: Re: [lttng-dev] major variations in perfomance figures >> >> On Tue, Mar 31, 2015 at 3:46 PM, Wolfgang Rostek <[email protected]> >> 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 >> > [email protected] >> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev >> >> >> >> -- >> Jérémie Galarneau >> EfficiOS Inc. >> http://www.efficios.com >> -- Jérémie Galarneau EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
