# Where is hot spot in cloud?
**URL:** https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082
**Category:** CMAQ
**Tags:** cmaq
**Created:** [November 29, 2025, 7:43am UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082 "2025-11-29T07:43:33Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@rzbbc](https://forum.cmascenter.org/u/rzbbc)
#### Post date: [November 29, 2025, 7:43am UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/1 "2025-11-29T07:43:33Z")
Hi there~ đ
Thank you for watching this post~
Iâm trying to optimize cldproc recently, and i locate an hotspot in subroutine RESCLD.
After some code insert and test, i realize that there exist an big load unbalance in RESCLD, and mostly in subroutine scavwdep.Unfortranately the code in scavwdep contains a loop with condition, which is hard for me to continue inserting code to watch it behavior.
I read the whole code in scavwdep.F, and my result is that it calculate `ALFA` in four different part, including `GC, AE, NR, TR`, and calculate `CEND` and `REMOV` respectly. During the calculation, subroutine `GETALPHA` is called to get `ALFA0, ALFA2, ALFA3`, and function `HLCONST` is called to get KH.
TWO existing optimize i found is below:
1ăseperate `ALFA` and `CEND&&REMOV`âs calc, and latter the `EXP(-ALFA * TAUCLD)` in CEND calculation could be vectorized. But it seems like that the code weigh not too much ratio.
2ăsearch algo in HLCONST is linear search, which can be optimize to hash(which i think maybe the core hotspot)
Another phenomena i found is that as timestep grows, the cost of cldproc grows. Is there any mechanics supporting this happens?
Does someone know where is the actual hotspot? Any sugguestion is appreciated.
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### Author:  [@rzbbc](https://forum.cmascenter.org/u/rzbbc)
#### Post date: [December 5, 2025, 6:55am UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/2 "2025-12-05T06:55:56Z")
i found the linear search in hlconst is the most hotspot.It deserves some dict optimization.Almost 50% optimize in scavwdep.
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### Author:  [@cjcoats](https://forum.cmascenter.org/u/cjcoats)
#### Post date: [December 5, 2025, 12:21pm UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/3 "2025-12-05T12:21:15Z")
In its way, this is much akin to what SMOKE is about: thirty years ago, emissions modeling was mostly a bunch of redundantly-repeated ad-hoc linear searches using character-string search-keys (the same search being repeated for every time step). The key insight was eliminating the redundancy by turning the ad-hoc problem into a âvectorâ problem where there were a fixed â sorted â orderings (a âvectorâ structure), using binary searches instead of linear, and wherever possible replacing character-string operations (which are horribly expensive) by integer operations wherever possible: then it comes down to the use of structured sparse operators (which in the case of SMOKE were sparse-matrix multiplications; for `HLCONST`, the operators are sparse-exponential). The same algorithmic-complexity ideas still apply.
The result was to replace an overnight supercomputer run by two minutes forty-three seconds on a desktop SPARC-II workstation.
Note that your hash-table idea is a bit of an improvement over the present, but still not as much improvement as you would get with a more structured vector approach.
[Note also that SMOKE today no longer follows all the improvements of the original]
FWIW â Carlie J. Coats, Jr.,Pl.D.
I/O API Author/Maintainer
original SMOKE Author
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### Author:  [@wong.david-c](https://forum.cmascenter.org/u/wong.david-c)
#### Post date: [December 9, 2025, 3:07pm UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/4 "2025-12-09T15:07:57Z")
Hi rzbbc,
Thanks for keep profiling the CMAQ model. I am not a cloud person but by examining the code, I saw two major subroutines: SCAVWDEP and AQ\_MAP, which are being called in RESCLD subroutine. In addition, there is a conditional statement âIF ( QCRGCOL .GT. 0.0 ) THENâ that determines whether they will be called or not. Load imbalance is inevitable. I have done a small test and this hypothesis has been confirmed.
You other observation is within HLCONST, there is an expensive operation, i.e. string comparison (Dr. Coats has pointed that out as well). I have devised a new way to handle that and I have done a quick test confirming the new modification does not alter results. If you donât mind, please contact me directly ([wong.david-c@epa.gov](mailto:wong.david-c@epa.gov)) and I will share the code with you so you can conduct an independent verification.
Cheers, David
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### Author:  [@rzbbc](https://forum.cmascenter.org/u/rzbbc)
#### Post date: [December 12, 2025, 6:57am UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/5 "2025-12-12T06:57:03Z")
Thank you for your reply~
I tried codes D.R. wong provided me, It turn out that âstructured vector approachâ can get some faster result in my computer than my previous realization~
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### Author:  [@rzbbc](https://forum.cmascenter.org/u/rzbbc)
#### Post date: [December 12, 2025, 7:01am UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/6 "2025-12-12T07:01:27Z")
Thank you for your reply. I have tested your code and the test result is in above post. Itâs turns out your idea in structured vector approach is right.
cheers, rzbbc.
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### Author:  [@Ben\_Murphy](https://forum.cmascenter.org/u/Ben_Murphy)
#### Post date: [December 18, 2025, 10:15pm UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/7 "2025-12-18T22:15:45Z")
This is great discussion. @cgnolte replaced the string comparisons in hlconst with integer comparisons about a year ago and it will likely be included in the next public CMAQ release.
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### Author:  [@wong.david-c](https://forum.cmascenter.org/u/wong.david-c)
#### Post date: [December 22, 2025, 1:36pm UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/8 "2025-12-22T13:36:57Z")
Hi rzbbc,
Thanks for performing an independent test. Hopefully the new code will be in the next release.
Cheers, David
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### Author:  [@system](https://forum.cmascenter.org/u/system)
#### Post date: [December 29, 2025, 1:37pm UTC](https://forum.cmascenter.org/t/where-is-hot-spot-in-cloud/6082/9 "2025-12-29T13:37:33Z")
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