V-Ray the log , it is built into the V-Ray System Alert. It has four levels mesedzh that are displayed on a background of a different color:
Red background - critical errors Green background - just warnings White background - rendering the current stats Black background - debug messages (for developers)
You have a green background, then it's just a warning.
warning Subpixel color mapping is on rendered result may have incorrect brightness.
warning: Performance loss: number of rendering threads ( 8) greater than number of light cache passes ( 4); some threads thread will be idle.
By Russ. - Warning: Loss of productivity: the amount of computing system flow (8) is greater than the amount of light cache passes (4), some threads will be idle.
Literally, it means that you are already 8 processing threads (most likely you have a family processor i7 with the HT , ie the 4th physical cores, each running two flow total of 8 processing threads), and in settings Light the Cache , in Number of passes, set share LC miscalculation on the part of all 4e. As a result, LC is considered only 4n flow, while the remaining flow system 4e - idle. Put the value of the Number of passes 8 and the message will disappear.