fix(benchmarks): use get_host_us_time() from native_sim timer_model.c

All previous approaches (clock_gettime, syscall, k_uptime, nsi_host_*)
returned 0 because native_sim intercepts them all at the binary level and
maps them to the simulated Zephyr clock (which doesn't advance during
CPU-bound loops).

get_host_us_time() is defined in timer_model.c (the native_sim hardware
timer model, compiled into the same binary) and calls CLOCK_MONOTONIC_RAW
directly from the OS timer model layer, BEFORE any Zephyr-level intercept.
It is the function native_sim itself uses to obtain real host time for
real-time mode synchronization -- it cannot be intercepted.

Returns µs * 1000 for nanosecond output.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: tbitcs

tests/benchmarks/kalman_benchmark/src/main.c

@@ -19,23 +19,15 @@
  * Zephyr kernel ticks which do NOT advance during CPU-bound loops.
  */
 #ifdef CONFIG_NATIVE_SIMULATOR
-/* native_sim replaces clock_gettime() AND syscall() with versions that
- * return simulated Zephyr time (stuck at 0 during CPU-bound loops).
- * nsi_host_clock_gettime() is native_sim's own escape hatch to the real
- * host OS clock, bypassing all simulated-time interception.
+/* native_sim's get_host_us_time() (defined in timer_model.c, compiled into
+ * the same native_sim binary) calls CLOCK_MONOTONIC_RAW directly from the
+ * OS timer model — it is the real host time in µs and is not intercepted
+ * by any simulated-time override.
  */
-#include <time.h>
-/* nsi_host_clock_gettime maps CLOCK_MONOTONIC to simulated time.
- * CLOCK_PROCESS_CPUTIME_ID measures actual CPU time consumed by this
- * process — it is OS-maintained, not interceptable by user-space time
- * simulation, and gives the true benchmark execution time.
- */
-extern int nsi_host_clock_gettime(int clk_id, struct timespec *tp);
+extern uint64_t get_host_us_time(void);
 static inline uint64_t bench_ns(void)
 {
-	struct timespec ts;
-	nsi_host_clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts);
-	return (uint64_t)ts.tv_sec * 1000000000ULL + (uint64_t)ts.tv_nsec;
+	return get_host_us_time() * 1000ULL;
 }
 #else
 /* On real hardware fall back to Zephyr timing API */

tests/benchmarks/pid_benchmark/src/main.c

@@ -22,13 +22,10 @@
 #include "arbiter_model.h"
 
 #ifdef CONFIG_NATIVE_SIMULATOR
-#include <time.h>
-extern int nsi_host_clock_gettime(int clk_id, struct timespec *tp);
+extern uint64_t get_host_us_time(void);
 static inline uint64_t bench_ns(void)
 {
-	struct timespec ts;
-	nsi_host_clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts);
-	return (uint64_t)ts.tv_sec * 1000000000ULL + (uint64_t)ts.tv_nsec;
+	return get_host_us_time() * 1000ULL;
 }
 #else
 #include <zephyr/timing/timing.h>