News from GPU parameters tuning

External framework integration

Tested Optuna optimization framework via O2tuner
Tree-structured Parzen Estimator (TPE) algorithm
- On each trial, for each parameter, TPE fits one Gaussian Mixture Model (GMM) l(x) to the set of parameter values associated with the best objective values
- And another GMM g(x) to the remaining parameter values
- It chooses the parameter value x that maximizes the ratio l(x)/g(x)

Results on FollowLoopers + CompressionStep0 (4 dimensions)

Dataset	Default step time	LHS algorithm solution time	TPE solution time
pp 2MHz	1097.26 ms ± 6.82 ms	971.22 ms ± 5.55 ms (-11.49%)	936.41 ms ± 5.93 ms (-14.66%)
PbPb 5kHz	224.94 ms ± 4.34 ms	195.63 ms ± 1.36 ms (-13.03%)	186.76 ms ± 3.08 ms (-16.97%)
PbPb 50kHz	1895.49 ms ± 25.84 ms	1736.86 ms ± 29.63 ms (-8.37%)	1881.87 ms ± 11.22 ms (-0.72%)

Results on SectorTracker step (16 dimensions)

Dataset	Default step time	LHS algorithm solution time	TPE solution time
pp 2MHz	2333.71 ms ± 20.06 ms	2206.02 ms ± 2.23 ms (-5.47%)	2094.66 ms ± 3.23 ms (-10.24%)
PbPb 5kHz	446.31 ms ± 1.87 ms	435.43 ms ± 1.66 ms (-2.44%)	435.20 ms ± 2.01 ms (-2.49%)
PbPb 50kHz	4519.54 ms ± 39.57 ms	4230.26 ms ± 5.40 ms (-6.40%)	4219.58 ms ± 4.71 ms (-6.64%)

Other parameters tuning (aside from grid and block size)

Tuned SectorTracker step including 5 additional parameters:
- PAR_NEIGHBOURS_FINDER_MAX_NNEIGHUP
- PAR_NEIGHBOURS_FINDER_UNROLL_GLOBAL
- PAR_NEIGHBOURS_FINDER_UNROLL_SHARED
- PAR_TRACKLET_SELECTOR_HITS_REG_SIZE
- PAR_SORT_STARTHITS
Total dimension: 21 parameters
Utilized o2tuner since it can handle all types of parameters
Found solution with step time: 4170.62 ms ± 3.07 ms
Step is 7.72% faster (previous solutions for this step: 6.40%, 6.64%)

Robustness of solutions

Simulated 2 more PbPb 50kHz datasets
Tested best parameters for SectorTracker step on these new datasets
So same parameters, different datasets with same "nature"

Dataset	Default step time	Best parameters time
PbPb_50kHz	4526.31 ms ± 33.60 ms	4163.49 ms ± 3.02 ms (-8.02%)
PbPb_50KHz_1	4765.86 ms ± 32.32 ms	4375.31 ms ± 2.76 ms (-8.19%)
PbPb_50KHz_2	4784.34 ms ± 23.60 ms	4404.51 ms ± 3.61 ms (-7.94%)

Overall improvement

Created dumps with best parameters for every step tested so far, per dataset
Measured sync time of standalone benchmark
Caveat: sync time fluctuates a bit, so difficult to have a precise measurement (single steps much more stable)

Dataset	Default sync time	Optimized sync time
pp 2MHz	10216.74 ms ± 71.58 ms	9874.28 ms ± 8.16 m (-3.35%)
PbPb 5kHz	2540.28 ms ± 3.45 ms	2440.55 ms ± 2.08 ms (-3.93%)
PbPb 50kHz	19679.88 ms ± 12.88 ms	18586.67 ms ± 30.42 ms (-5.55%)

To-Dos

Investigate more on robustness
- Measure other steps
- Measure overall improvement on sync time
Tune rest of the steps
Test for other IRs
Try other algorithms
...?