[geom] Add cache layer for TGeoParallelWorld safeties in TGeoNavigator #16470
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This commit provides an (optional) optimization to reduce the cost of safety evaluations associated with TGeoParallelWorld. The approach consists in the introduction of additional cache-state in TGeoNavigator. This state remembers the last location for which TGeoParallelWorld::Safety was evaluated, together with the corresponding value returned. Since TGeoNavigator follows the evolution of tracks step-by-step, we have some sort of history-locality. This means that the cache-state has a high-probability of being relevant for multiple track locations in a row. The optimization proposed here is orthogonal to other improvements. It adds on top of algorithmic improvements within TGeoParallelWorld (bounding volume hierarchies, see separate PR), gaining a few extra percent in speed. By default, the new feature is not enabled by default for backward compatibility. Once fully verified, we can make it the default mode. That said, in ALICE simulations, the caching did not modify stepping behaviour and yielded identical results compared to not doing the caching.
agheata
reviewed
Sep 19, 2024
Test Results 12 files 12 suites 2d 23h 25m 55s ⏱️ Results for commit c19ac8e. ♻️ This comment has been updated with latest results. |
take away factor
agheata
approved these changes
Sep 20, 2024
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This commit provides an (optional) optimization to reduce the cost of safety evaluations associated with TGeoParallelWorld.
The approach consists in the introduction of additional cache-state in TGeoNavigator. This state remembers the last location for which TGeoParallelWorld::Safety was evaluated, together with the corresponding value returned.
Since TGeoNavigator follows the evolution of tracks step-by-step, we have some sort of history-locality. This means that the cache-state has a high-probability of being relevant for multiple track locations in a row.
The optimization proposed here is orthogonal to other improvements. It adds on top of algorithmic improvements within TGeoParallelWorld (bounding volume hierarchies, see separate PR), gaining a few extra percent in speed.
By default, the new feature is not enabled by default for backward compatibility. Once fully verified, we can make it the default mode.
That said, in ALICE simulations, the caching did not modify stepping behaviour and yielded identical results compared to not doing the caching.
Checklist: