Re: Linux Kernel Markers - performance characterization with large IO load on large-ish system

[Joshua Root <jmr@xxxxxxxxxxxxxxxxxx>]

Ingo Molnar wrote:
> actually, the pure marker overhead seems to be a regression:
>
> Kernel Options       Min val    Avg val    Max val    Std Dev
> > - markers - bt cfg  15.349127  16.169459  16.372980   0.184417
> > + markers - bt cfg  15.280382  16.202398  16.409257   0.191861
>
> why isnt the marker near zero-cost as it should be? (as long as they are 
> enabled but are not in actual use) 2% increase is _ALOT_.

The increase in the mean is actually 0.033, or 0.2%.

> So there's something wrong going on - either markers have unacceptably 
> high cost, or the measurement is not valid.

The third option is that the measurement just needs to be done more 
times. The standard error in the mean for the + markers case is
0.191861 / sqrt(10) = 0.061, which is twice the size of the difference 
being measured.
--
Joshua Root,  jmr AT gelato.unsw.edu.au
http://www.gelato.unsw.edu.au
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