As RfK converts the Katana scene graph into the Rix scene graph for rendering it will do so in parallel, spawning new threads at location branches. The default is "all on" meaning it will fork on every child location in the scene which is unlikely to be ideal for most scenes but allows for deeper control by the author for control of parallelism. There are are varying levels of control which will take some adjustment to come up with a configuration that works with your pipeline and subsequently for individual scenes.
Understand that some branches processed serially may improve time to first pixel (the time it takes for the render to begin sending pixels) and is very much scene dependent, but important to understand that parallel traversal on everything may be costly.
Currently there are three ways to set the number of render threads in RfK. The first two will trigger a "
-t:#" addition to the command line arguments for prman which, by RenderMan definition, will override any thread specification in the RIB (the third option).
Ways to set thread count, in order of precedence:
--threads3d" command line parameter in batch mode).
How and where to set these values are detailed below.
Below is a screen capture of the preferences interactiveRenderThreadsOverride and interactiveRenderThreads3D (equivalent to the use of the "
--threads3d" command line parameter in batch mode). If you want to definitively set the number of render threads this will be the place to do it. Set interactiveRenderThreadsOverride = Yes and set the value of interactiveRenderThreads3D to your desired threads:
The attribute renderSettings.renderThreads must be set via AttributeSet or OpScript as it is not exposed in RenderSettings. Below is an example of setting the attribute with an AttributSet node:
The prman option for limits.threads is set via the Options section of the PrmanGlobalStatements node:
This attribute translates literally to RIB:
Option "limits" "int threads" [N]
As it is lowest in the precedence list, this thread option is overridden if either (1) preferences or (2) render settings have a thread value enabled.
In all cases, if a value of 0 (zero) is given to prman then all CPUs will be utilized for rendering. If a negative value (-N) is specified then prman will use all but N CPUs for rendering.