[lttng-dev] major variations in perfomance figures

[Jérémie Galarneau]

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.
>
>
>
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-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com