[Development] Using string literals in autotests

[Giuseppe D'Angelo]

Il 28/03/24 12:14, Friedemann Kleint via Development ha scritto:
> Hi,
> 
> I'd say performance should be a consideration for autotests since they
> are compiled and run over and over again in the CI. So, string theory
> should be applied to avoid unnecessary conversions and allocations. Even
> it is considered a minor optimization, it will have an impact on energy
> consumption & CO2 emission in the end, IMO.

Diminishing CI run time and saving energy is certainly an excellent 
goal, but this is starting from the wrong end. A qWait(100), or a few 
extra memory allocations, or a wrong algorithm will easily squander any 
saving that you could gain when optimally comparing strings. You'd need 
to micro-optimize so much that it simply isn't worth the effort.



Here's another hot take. Consider:

* A(X) = how much energy is wasted when a random CI node goes bust for X 
hours -- and that makes integrations fail on all the CI -- although the 
other nodes did build+test the code. (This very morning: WASM is 
blocking qtbase/dev integrations)

* B = how much time/energy you save, per CI integration, by 
micro-optimizing every string construction/comparison



How much work is necessary to achieve B? And then, how many CI runs are 
necessary to offset the waste that e.g. 24h of CI downtime cause?

I feel we're easily into the man-years of effort (maybe this can be 
partially tooled, but then, the tooling needs to constantly chase up 
changes in QtCore), and dozens of thousands of CI runs. Which makes the 
effort pointless: it takes years to get thousands of CI runs (qtbase 
integrations take ~2h?), during which the CI will go bust *again*, 
squandering all your savings.


My 2 c,
-- 
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - Trusted Software Excellence

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