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Panel: Properties > Render Properties > Performance

2.9 <2.8>

Performance

Threads

Threads Mode

Auto-detect

Automatically chooses the amount of threads to match the number of logical processors on your computer.

Fixed

Manually choose the amount of threads to use for rendering. This can be useful for example, if you want to use your computer while rendering, you can set the property to a thread count lower the amount of logical processors on your computer.

Threads

Number of CPU threads to use simultaneously while rendering (for multi-core/CPU systems).

Tiles

Tile X/Y

The size of the tiles for rendering.

Depending on what device you are using for rendering, different tile sizes can give faster renders. For CPU rendering smaller tiles sizes (like 32 × 32) tend to be faster, while for GPU rendering larger tile sizes give a better performance (like 256 × 256).

Order

Order of rendering tiles. This does not significantly affect the performance.

Center

Right to Left

Left to Right

Top to Bottom

Bottom to Top

Hilbert Spiral

Progressive Refine

Instead of rendering each tile until it has finished every sample, refine the whole image progressively. Note that progressive rendering is slightly slower than tiled rendering, but time can be saved by manually stopping the render when the noise level is low enough.

For rendering animations it is best to disable this feature, as stopping a frame early is not possible.

Acceleration Structure

Use Spatial Splits

Spatial splits improve the rendering performance in scenes with a mix of large and small polygons. The downsides are longer BVH build times and slightly increased memory usage.

Use Hair BVH

Use a special type of BVH for rendering hair. The bounding boxes are not axis aligned allowing a spatially closer fit to the hair geometry. Disabling this option will reduce memory, at the cost of increasing hair render time.
BVH

BVH Time Steps

Split BVH primitives by this number of time steps to speed up render time in cost of memory.

Final Render

Save Buffers

Saves all render layers and passes to the temp directory on a drive, and reads them back after rendering has finished. This saves memory (RAM) usage during rendering, particularly when using many render layers and passes. This can be read back in the Compositor and Image editor by using Layers.
Layers

Persistent Images

Keep image data in memory after rendering, for faster re-renders at the cost of extra memory usage when performing other tasks in Blender.

Viewport

Pixel Size

Option to control the resolution for viewport rendering. Allows you to speed up viewport rendering, which is especially useful for displays with high DPI.

Start Pixels

Resolution to start rendering preview at, progressively increase it to the full viewport size.