bench: microsecond timing via tools/timeit, toybox oracle, words to 10M lines

benchmarks/tools/timeit.c

@@ -0,0 +1,59 @@
+/* timeit — run a command once and print its elapsed wall time in µs.
+ *
+ * The benchmark harness races fastwc against several wc implementations.
+ * Timing both sides by wrapping the command in `date +%s%N` forks added
+ * over a millisecond of noise per sample — more than the whole run on a
+ * small case — so every sub-millisecond race was decided by fork jitter,
+ * not by speed. This helper measures a plain fork + exec + wait with
+ * clock_gettime and prints the elapsed microseconds on its own stdout.
+ * The timed command's output is discarded, exactly as the old date
+ * wrapper did, so capture_count (which runs the command directly) is the
+ * only path that sees real output.
+ *
+ * usage: timeit <cmd> [arg...]
+ */
+#define _POSIX_C_SOURCE 200809L
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+    struct timespec t0, t1;
+    pid_t pid;
+    int nullfd;
+
+    if (argc < 2)
+        return 2;
+
+    clock_gettime(CLOCK_MONOTONIC, &t0);
+
+    pid = fork();
+    if (pid < 0)
+        return 2;
+    if (pid == 0)
+    {
+        /* child: run the timed command with its output thrown away */
+        nullfd = open("/dev/null", O_WRONLY);
+        if (nullfd >= 0)
+        {
+            dup2(nullfd, STDOUT_FILENO);
+            dup2(nullfd, STDERR_FILENO);
+            close(nullfd);
+        }
+        execvp(argv[1], &argv[1]);
+        _exit(127);
+    }
+
+    if (waitpid(pid, NULL, 0) < 0)
+        return 2;
+    clock_gettime(CLOCK_MONOTONIC, &t1);
+
+    printf("%lld\n",
+           ((long long)(t1.tv_sec - t0.tv_sec) * 1000000000LL
+            + (t1.tv_nsec - t0.tv_nsec)) / 1000);
+    return 0;
+}