Identifying GPU, Render Thread, and Game Thread issues
There are several features of UE4 in place which allow effects artists to trouble shoot performance issues. First off, identifying where your effects are creating bottlenecks will go a long way towards optimizing the correct issue, thereby retaining visual integrity/quality.
One way to monitor for issues while playing through levels is to pull up the STAT UNIT debug overlay.
Launch the game.
Press the ` key and enter
stat unit into the Console.
stat unit command displays the time spent for the current frame on the Game Thread, the time spent for the Render thread, and the time spent for the GPU. It is possible to monitor the different times updated by stat unit to see areas of the level with performance issues.
Keep an eye on the different thread times. If your target framerate is 30fps, all threads should remain below 33.3ms.
If any thread goes over the 33ms and your particles are a suspected culprit, you can use the
STAT PARTICLES command to gauge particle times on the different threads.
STAT PARTICLES lists out multiple statistics relative to Game Thread and Render Thread. Pay attention to Draw Calls (Render Thread) and Tick Time (Game Thread).