From 0e610831d584d9485eb0655168d08d8234bbb555 Mon Sep 17 00:00:00 2001
From: WangJian <wangjian161@huawei.com>
Date: Wed, 9 Feb 2022 10:48:58 +0800
Subject: [PATCH] qemu-nbd: make native as the default aio mode

When the file system is dealing with multithreading concurrent writing to a file,
the performance will be degraded because of the lock.
At present, the default AIO mode of QEMU NBD is threads. In the case of large blocks,
because IO is divided into small pieces and multiple queues, it will become multithreading
concurrent writing the same file. Due to the file system, the performance will be greatly reduced.
If you change to native mode, this problem will not exist.

Signed-off-by: wangjian161 <wangjian161@huawei.com>
---
 qemu-nbd.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/qemu-nbd.c b/qemu-nbd.c
index 186e6468b1..acccf2977f 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -843,6 +843,10 @@ int main(int argc, char **argv)
     trace_init_file();
     qemu_set_log(LOG_TRACE, &error_fatal);
 
+    if (!seen_aio && (flags & BDRV_O_NOCACHE)) {
+        flags |= BDRV_O_NATIVE_AIO;
+    }
+
     socket_activation = check_socket_activation();
     if (socket_activation == 0) {
         if (!sockpath) {
-- 
2.27.0