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UE CPU Cooler
Unreal Engine’s frame limiter avoids sleeping all the way to the target frame time.
It first sleeps for most of the wait:
SleepNoStats(WaitTime - 0.002f);
This leaves about 2 ms of slack, because OS sleep calls can oversleep due to scheduler granularity and wake-up latency.
Then UE waits for the exact frame boundary with:
while (FPlatformTime::Seconds() < WaitEndTime)
{
SleepNoStats(0);
}
On generic platforms, SleepNoStats(0) becomes sched_yield(). So the thread does not request a timed sleep; it simply gives up its current time slice and checks again.
This improves frame pacing because UE is less likely to wake up after the target time. The cost is that the final ~2 ms keeps the CPU relatively active, causing extra scheduler work and higher power usage.
In short, UE trades CPU activity for more accurate frame pacing.
If your platform is power-sensitive, you can replace the final sched_yield loop with SleepNoStats(0.002f) to avoid repeatedly yielding, at the cost of less precise timing.