MMC Request Latency Tracing: Absent Kernel Tracepoint for SDHCI Completion Events
Goal Isolate the SDHCI controller's per-request completion latency from ext4 journaling and page-cache overhead during random write workloads on Raspberry Pi 4. Constraints and Uncertainty The upstream kernel exposes no tracepoint for mmc_request_done or SDHCI interrupt latency, so ftrace cannot attribute latency spikes to the controller versus the card's in
raspberrypi