test/sqpoll-sleep: ensure WAKEUP flag is read correctly

Rewrite this test to be a bit better:

- Read wakeup properly with IO_URING_READ_ONCE()
- Check if wakeup has been seen
- Check elapsed time before wakeup flag is seen
- Prepare and push a nop request first, to ensure the thread is up
  and running

Hopefully this will fix the quirks with this test.

Link: #1207
Signed-off-by: Jens Axboe <axboe@kernel.dk>

test/sqpoll-sleep.c

@@ -14,32 +14,63 @@
 int main(int argc, char *argv[])
 {
 	struct io_uring_params p = {};
+	struct io_uring_sqe *sqe;
+	struct io_uring_cqe *cqe;
 	struct timeval tv;
 	struct io_uring ring;
+	unsigned long elapsed;
+	bool seen_wakeup;
 	int ret;
 
 	if (argc > 1)
-		return 0;
+		return T_EXIT_SKIP;
 
 	p.flags = IORING_SETUP_SQPOLL;
-	p.sq_thread_idle = 10000;
+	p.sq_thread_idle = 100;
 
 	ret = io_uring_queue_init_params(1, &ring, &p);
 	if (ret) {
 		if (geteuid()) {
 			printf("%s: skipped, not root\n", argv[0]);
-			return 0;
+			return T_EXIT_SKIP;
 		}
 		fprintf(stderr, "queue_init=%d\n", ret);
-		return 1;
+		return T_EXIT_FAIL;
 	}
 
+	sqe = io_uring_get_sqe(&ring);
+	io_uring_prep_nop(sqe);
+	io_uring_submit(&ring);
+
+	ret = io_uring_wait_cqe(&ring, &cqe);
+	if (ret) {
+		fprintf(stderr, "wait_cqe: %d\n", ret);
+		return T_EXIT_FAIL;
+	}
+	io_uring_cqe_seen(&ring, cqe);
+
+	elapsed = 0;
+	seen_wakeup = false;
 	gettimeofday(&tv, NULL);
 	do {
-		usleep(100000);
-		if ((*ring.sq.kflags) & IORING_SQ_NEED_WAKEUP)
-			return 0;
-	} while (mtime_since_now(&tv) < 1000);
+		usleep(100);
+		if (IO_URING_READ_ONCE(*ring.sq.kflags) & IORING_SQ_NEED_WAKEUP) {
+			seen_wakeup = true;
+			break;
+		}
+		elapsed = mtime_since_now(&tv);
+	} while (elapsed < 1000);
+
+	if (!seen_wakeup) {
+		fprintf(stderr, "SQPOLL didn't flag wakeup\n");
+		return T_EXIT_FAIL;
+	}
+
+	/* should be around 100 msec */
+	if (elapsed < 90 || elapsed > 110) {
+		fprintf(stderr, "SQPOLL wakeup timing off %lu\n", elapsed);
+		return T_EXIT_FAIL;
+	}
 
-	return 1;
+	return T_EXIT_PASS;
 }