“iOS 26 + BGContinuedProcessingTask: Why does a CPU/ML-intensive job run 4-5× slower in background?”
Hello All, I’m a mobile-app developer working with iOS 26+ and I’m using BGContinuedProcessingTask to perform background work. My app’s workflow includes the following business logic: Loading images via PHImageRequest. Using a CLIP model to extract image embeddings. Using an .mlmodel-based model to further process those embeddings. For both model inferences I set computeUnits = .cpuAndNeuralEngine. When the app is moved to the background, I observe that the same workload(all three workload) becomes on average 4-5× slower than when the app is in the foreground. In an attempt to diagnose the slowdown, I tried to profile with Xcode Instruments, but since a debugger was attached, the performance in background appeared nearly identical to foreground. Even when I detached the debugger, the measured system resource metrics (process CPU usage, system CPU usage, memory, QoS class, thermal state) showed no meaningful difference. Below are some of the metrics I captured: Process CPU: 177% (Foreground) → 153% (B