Simulation threads, substeps, frame rate, CPU load, and simulation speed are important variables in conjunction with RealFlow. Let's clear up the relations between all these terms.
Simulation Threads
This number represents your computer's number of CPU's or cores:
- If your computer supports hyper-threading you will see a higher value.
- Threads can be adjusted for each scene individually under → Simulation Options > General.
Under some circumstances you will notice that RealFlow uses only a fraction of the available cores and CPU load is just around 10%. This is typically the case with low-resolution fluid simulations:
- RealFlow requires some time to split the simulation into threads.
- With just a few thousands of particles it is normally better to reduce the number of threads.
- The more particles, the better the computer's performance.
- In simulations with several millions of particles, all threads are used and CPU load is around 95%.
Another thing you will observe is a performance drop at the beginning of a simulation or between two frames:
- When a simulation starts RealFlow prepares lots of things and these processes are all single-threaded.
- Saving simulation data is also single-threaded and hardly uses any CPU power.
With more than 32 threads you will hardly see any performance boosts, because computer systems do not scale linearly and there is always a limit.
FPS Rate and Substeps
A common question is why simulations with a high FPS rate require less substeps? The answer is precision. The length of a single substep is calculated as
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