feat: NPU metrics logger daemon

[Sam Freund (samfreund-qc)]

Summary

Adds QcPerfNpuLogger, a standalone systemd-compatible daemon that uses the public qcperf_* API to continuously sample all four NPU metrics and write a point-in-time snapshot to /var/log/qcperf/npu_metrics.log once per second.

What it does

The daemon connects to QC_PERF_BACKEND_DSP_NPU, samples at 100 ms intervals, and fires a streaming callback every 1000 ms. Each callback atomically replaces the output file (write to .npu_metrics.tmp, then rename(2)) so readers never observe a partial write. The most recent sample per metric within each streaming window is kept; earlier samples are discarded.

Output format:

Q6 Utilization:42.50
Q6 Clock:614400.00
HVX Utilization:12.30
HMX Utilization:8.70

Files added

File	Purpose
qcperf/npu_logger/src/qcperf_npu_logger.c	Daemon implementation (main, callbacks, helpers)
qcperf/npu_logger/systemd/qcperf-npu-logger.service	systemd unit with hardened sandbox
qcperf/npu_logger/CMakeLists.txt	Build rules, opt-in via -DBUILD_NPU_LOGGER=ON

Build

cmake -S qcperf -B build-linux-aarch64-release \
    -DTARGET_ARCH=linux-aarch64 \
    -DCMAKE_BUILD_TYPE=Release \
    -DProjectVersion="0.1.0.0" \
    -DBACKENDS="CPU;NPU;DUMMY" \
    -DBUILD_NPU_LOGGER=ON
cmake --build build-linux-aarch64-release

The target is off by default. Enabling it without NPU in BACKENDS emits a CMake warning and skips the build gracefully.

Runtime requirement

/usr/lib/libcdsprpc.so must be present on the target device. If absent, the dynamic linker fails at process startup — this is a constraint of the underlying FastRPC transport, not something the daemon can work around.

systemd unit highlights

• ProtectSystem=strict + LogsDirectory=qcperf (creates /var/log/qcperf before the namespace is set up, required for first install)
• PrivateTmp=true, NoNewPrivileges=true
• Restart=on-failure with a 5 s back-off
• Logs to the systemd journal via SyslogIdentifier=qcperf-npu-logger

Testing

Run on a Qualcomm Linux ARM64 device with libcdsprpc.so present:

# Start the daemon manually
/usr/bin/QcPerfNpuLogger &

# Verify output
cat /var/log/qcperf/npu_metrics.log

# Or via systemd
systemctl enable --now qcperf-npu-logger
journalctl -u qcperf-npu-logger -f

Checklist

• BSD 3-Clause copyright header present
• Single exit point per function
• All variables declared at top of function (C89 style)
• No goto, no always-true loops
• Yoda-style null checks (NULL == ptr)
• calloc used instead of malloc; pointers set to NULL after free
• snake_case / PascalCase / UPPER_CASE naming conventions followed
• Doxygen comments on all functions
• clang-format — not available on the development host; please run before merge: clang-format -i qcperf/npu_logger/src/qcperf_npu_logger.c