This page gives some basic information about IPR within Maya and how to incorporate the interactive renderer into your workflow.
IPR is Chaos Group's interactive rendering engine that can utilize both CPU and GPU hardware acceleration to see updates to the rendered image in real time as objects, lights, and materials are edited within the scene.
This section of the V-Ray for Maya documentation also includes the following pages:
||Status Line|| > Maya IPR button
||Viewport|| > Renderer menu > V-Ray IPR
IPR can be selected within the V-Ray VFB window. IPR mode is also supported within the Maya viewport.
To start using IPR, click the IPR button (IPR render the current frame) found in the Rendering icons section of the Maya Status Line UI element. To switch a viewport's renderer to IPR, open the Renderer menu from the viewport and select V-Ray IPR.
Maya 2016+ Color Management and V-Ray IPR
With the additional setting for Color Management in Maya 2016 or later, it is possible that color banding may be visible within the viewport when using IPR as the renderer. This can be resolved by Disabling Maya's Color Management from its Preferences and confirming that Convert to sRGB is Enabled under Render Settings window > IPR tab > Viewport > sRGB.
Note: This banding issue is localized to IPR rendering in a Maya Viewport. It is more likely to be visible when using a V-Ray Physical Camera with Vignetting enabled.