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