move duplicated io_uring code into io_uring.h

common.h

 #pragma once
 
+#define likely(x) __builtin_expect(!!(x), 1)
 #define unlikely(x) __builtin_expect(!!(x), 0)
 
 extern size_t warmup, iterations;

io-uring-no-syscall.c

@@ -4,26 +4,18 @@
 #include <stdlib.h>
 
 #include "common.h"
+#include "io_uring.h"
 #include "stopwatch.h"
 
 struct io_uring ring;
 
-void init(__attribute__((unused)) int fd) {
-	int res = io_uring_queue_init(16, &ring, IORING_SETUP_SQPOLL);
-	if (res < 0) {
-		errno = res;
-		err(EXIT_FAILURE, "io_uring_setup failed");
-	}
-}
+void init(__attribute__((unused)) int fd) { io_uring_init_sqpoll(&ring); }
 
 void do_write(int fd, const void *buf, size_t count) {
-	start_watch();
-	struct io_uring_sqe *sqe = io_uring_get_sqe(&ring);
-	while (unlikely(!sqe)) {
-		sqe = io_uring_get_sqe(&ring);
-	}
+	struct io_uring_sqe *sqe = sqpoll_ring_get_sqe(&ring);
 	io_uring_prep_write(sqe, fd, buf, count, 0);
 
+	start_watch();
 	int res = io_uring_submit(&ring);
 
 	struct io_uring_cqe *cqe;
@@ -32,11 +24,7 @@ void do_write(int fd, const void *buf, size_t count) {
 
 	stop_watch();
 
-	if (res < 0) {
-		err(EXIT_FAILURE, "io_submit failed");
-	}
+	if (res < 0) err(EXIT_FAILURE, "io_submit failed");
 
-	if (cqe->res < 0) {
-		err(EXIT_FAILURE, "write request failed");
-	}
+	if (cqe->res < 0) err(EXIT_FAILURE, "write request failed");
 }

io-uring-sqpoll.c

@@ -4,29 +4,19 @@
 #include <stdlib.h>
 
 #include "common.h"
+#include "io_uring.h"
 #include "stopwatch.h"
 
 struct io_uring ring;
 
-void init(__attribute__((unused)) int fd) {
-	int res = io_uring_queue_init(16, &ring, IORING_SETUP_SQPOLL);
-	if (res < 0) {
-		errno = res;
-		err(EXIT_FAILURE, "io_uring_setup failed");
-	}
-}
+void init(__attribute__((unused)) int fd) { io_uring_init_sqpoll(&ring); }
 
 void do_write(int fd, const void *buf, size_t count) {
-	start_watch();
-
-	struct io_uring_sqe *sqe = io_uring_get_sqe(&ring);
-	while (unlikely(!sqe)) {
-		sqe = io_uring_get_sqe(&ring);
-	}
+	struct io_uring_sqe *sqe = sqpoll_ring_get_sqe(&ring);
 	io_uring_prep_write(sqe, fd, buf, count, 0);
 
+	start_watch();
 	int res = io_uring_submit_and_wait(&ring, 1);
-
 	stop_watch();
 
 	if (res < 0) {
@@ -35,11 +25,8 @@ void do_write(int fd, const void *buf, size_t count) {
 
 	struct io_uring_cqe *cqe;
 	res = io_uring_peek_cqe(&ring, &cqe);
-	if (res < 0) {
-		err(EXIT_FAILURE, "io_uring_peek_cqe failed");
-	}
 
-	if (cqe->res < 0) {
-		err(EXIT_FAILURE, "write request failed");
-	}
+	if (res < 0) err(EXIT_FAILURE, "io_uring_peek_cqe failed");
+
+	if (cqe->res < 0) err(EXIT_FAILURE, "write request failed");
 }

io_uring.h

+#pragma once
+
+#include <err.h>
+#include <liburing.h>
+
+#include "common.h"
+
+#define GET_SQE_ATTEMPTS 1000000
+struct io_uring_sqe* sqpoll_ring_get_sqe(struct io_uring* ring) {
+	struct io_uring_sqe* sqe;
+	size_t attempts = 0;
+	for (;;) {
+		sqe = io_uring_get_sqe(ring);
+		if (likely(sqe)) return sqe;
+
+		++attempts;
+
+		if (attempts < GET_SQE_ATTEMPTS) continue;
+
+		errx(EXIT_FAILURE, "failed to get sqe after %d", GET_SQE_ATTEMPTS);
+	}
+}
+
+#define SQPOLL_RING_ENTRIES 16
+
+void io_uring_init_sqpoll(struct io_uring* ring) {
+	int res = io_uring_queue_init(SQPOLL_RING_ENTRIES, ring, IORING_SETUP_SQPOLL);
+	if (res < 0) {
+		errno = res;
+		err(EXIT_FAILURE, "io_uring_setup failed");
+	}
+}