debug: debug_stream: log per-core utilization from idle thread load

Keep the per-thread stack and cpu LOG_DBG print and add a separate
LOG_INF that fires only for the Zephyr idle thread. The info-level
print reports per-core CPU utilization calculated as the inverse of
the idle thread load percentage.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

Author: kv2019i

src/debug/debug_stream/Kconfig

@@ -45,6 +45,15 @@ config SOF_DEBUG_STREAM_THREAD_INFO_INTERVAL
 	  Decides how often thread info runs and checks execution cycle
 	  statistics and stack usage.
 
+config SOF_DEBUG_STREAM_THREAD_INFO_TOTAL_CPU_LOAD_TO_LOG
+	bool "Print summarized total CPU load to log subsystem"
+	depends on SOF_DEBUG_STREAM_THREAD_INFO
+	default y
+	help
+	  In addition to printing thread statistics to debug stream,
+	  print the total CPU load (sum of all threads) to
+	  the logging system.
+
 config SOF_DEBUG_STREAM_TEXT_MSG
 	bool "Enable text message sending through Debug-Stream"
 	help

src/debug/debug_stream/debug_stream_thread_info.c

@@ -225,6 +225,13 @@ static void thread_info_cb(const struct k_thread *cthread, void *user_data)
 		tinfo->name, tinfo->stack_usage * 100U / 255,
 		tinfo->cpu_usage * 100U / 255);
 
+	/* .is_idle depends on CONFIG_SMP */
+#if defined(CONFIG_SOF_DEBUG_STREAM_THREAD_INFO_TOTAL_CPU_LOAD_TO_LOG) && defined(CONFIG_SMP)
+	if (thread->base.is_idle)
+		LOG_INF("core %u utilization %u%%", ud->core,
+			100U - tinfo->cpu_usage * 100U / 255);
+#endif
+
 	ud->thread_count++;
 }