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

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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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