xen-console: Optimize console_display_thrd

Optimize console_display_thrd by removing the inner loop that copies
data from the console buffer to the output buffer. Instead, calculate
the size of the data to be copied and print it in one go.

Signed-off-by: Mykyta Poturai <[email protected]>
Reviewed-by: Dmytro Firsov <[email protected]>
Reviewed-by: Volodymyr Babchuk <[email protected]>

xen-console-srv/src/xen_console.c

@@ -367,9 +367,8 @@ static void console_display_thrd(void *p1, void *p2, void *p3)
 	ARG_UNUSED(p3);
 	struct xen_domain_console *console = p1;
 	const struct shell *shell = p2;
-	/* Buffer input a little */
-	char buf[32];
-	int read;
+	size_t buf_pos, prod_buf_pos;
+	int size;
 
 	shell_info(shell, "Attached to a domain console");
 
@@ -387,19 +386,24 @@ static void console_display_thrd(void *p1, void *p2, void *p3)
 		}
 
 		while (console->int_cons < console->int_prod) {
-			read = 0;
-			memset(buf, 0, sizeof(buf));
-
-			/* TODO: There is a room for optimization.... */
-			while (console->int_cons < console->int_prod &&
-			       read < sizeof(buf) - 1) {
-				size_t buf_pos = (console->int_cons++) &
-					(XEN_CONSOLE_BUFFER_SZ - 1);
-				buf[read++] = console->int_buf[buf_pos];
-			}
-			if (read) {
-				shell_fprintf(shell, SHELL_NORMAL, "%s", buf);
+			buf_pos = (console->int_cons) &
+				(XEN_CONSOLE_BUFFER_SZ - 1);
+			prod_buf_pos = (console->int_prod) &
+				(XEN_CONSOLE_BUFFER_SZ - 1);
+			/* int_buf is a circular buffer so we need to check for
+			 * the wrap around condition to print it safely.
+			 * In the case of the wrap around condition, we first
+			 * print from the buf_pos to the end of the buffer,
+			 * and then continue printing from the beginning of the buffer.
+			 */
+			if (buf_pos < prod_buf_pos) {
+				size = prod_buf_pos - buf_pos;
+			} else {
+				size = XEN_CONSOLE_BUFFER_SZ - buf_pos;
 			}
+			shell_fprintf(shell, SHELL_NORMAL, "%.*s", size,
+						&console->int_buf[buf_pos]);
+			console->int_cons += size;
 		}
 		k_mutex_unlock(&console->lock);
 	}