| 2017-10-21 14:32:56 |
Carl Brassey |
description |
Description of problem
-------------------------
In my latest topic, I reported a bug relate to QEMU's websocket:
https://bugs.launchpad.net/qemu/+bug/1718964
It has been fixed but someone mentioned that he met the same problem when using QEMU with a standalone websocket proxy.
That makes me confused because in that scenario QEMU will get a "RAW" VNC connection.
So I did a test and found that there indeed existed some problems. The problem is:
When the client's network is poor (on a low speed WAN), QEMU still sends a lot of data to the websocket proxy, then the client get stuck. It seems that only QEMU has this problem, other VNC servers works fine.
Environment
-------------------------
All of the following versions have been tested:
QEMU: 2.8.1.1 / 2.9.1 / 2.10.1 / master (Up to date)
Host OS: Ubuntu 16.04 Server LTS / CentOS 7 x86_64_1611
Websocket Proxy: websockify 0.6.0 / 0.7.0 / 0.8.0 / master
VNC Web Client: noVNC 0.5.1 / 0.61 / 0.62 / master
Other VNC Servers: TigerVNC 1.8 / x11vnc 0.9.13 / TightVNC 2.8.8
Steps to reproduce:
-------------------------
100% reproducible.
1. Launch a QEMU instance (No need websocket option):
qemu-system-x86_64 -enable-kvm -m 6G ./win_x64.qcow2 -vnc :0
2. Launch websockify on a separate host and connect to QEMU's VNC port
3. Open VNC Web Client (noVNC/vnc.html) in browser and connect to websockify
4. Play a video (e.g. Watch YouTube) on VM (To produce a lot of frame buffer update)
5. Limit (e.g. Use NetLimiter) the client inbound bandwidth to 300KB/S (To simulate a low speed WAN)
6. Then client's output gets stuck(less than 1 fps), the cursor is almost impossible to move
7. Monitor network traffic on the proxy server
Current result:
-------------------------
Monitor Downlink/Uplink network traffic on the proxy server
(Refer to the attachments for more details).
1. Used with QEMU
- D: 5.9 MB/s U: 5.7 MB/s (Client on LAN)
- D: 4.3 MB/s U: 334 KB/s (Client on WAN)
2. Used with other VNC servers
- D: 5.9 MB/s U: 5.6 MB/s (Client on LAN)
- D: 369 KB/s U: 328 KB/s (Client on WAN)
It is found that when the client's network is poor, all the VNC servers (tigervnc/x11vnc/tightvnc)
will reduce the VNC data send to websocket proxy (uplink and downlink symmetry), but QEMU never drop any frames and still sends a lot of data to websockify, the client has no capacity to accept so much data, more and more data are accumulated in the websockify, then it crashes.
Expected results:
-------------------------
When the client's network is poor (WAN), QEMU will reduce the VNC data send to websocket proxy. |
Description of problem
-------------------------
In my latest topic, I reported a bug relate to QEMU's websocket:
https://bugs.launchpad.net/qemu/+bug/1718964
It has been fixed but someone mentioned that he met the same problem when using QEMU with a standalone websocket proxy.
That makes me confused because in that scenario QEMU will get a "RAW" VNC connection.
So I did a test and found that there indeed existed some problems. The problem is:
When the client's network is poor (on a low speed WAN), QEMU still sends a lot of data to the websocket proxy, then the client get stuck. It seems that only QEMU has this problem, other VNC servers works fine.
Environment
-------------------------
All of the following versions have been tested:
QEMU: 2.8.1.1 / 2.9.1 / 2.10.1 / master (Up to date)
Host OS: Ubuntu 16.04 Server LTS / CentOS 7 x86_64_1611
Websocket Proxy: websockify 0.6.0 / 0.7.0 / 0.8.0 / master
VNC Web Client: noVNC 0.5.1 / 0.61 / 0.62 / master
Other VNC Servers: TigerVNC 1.8 / x11vnc 0.9.13 / TightVNC 2.8.8
Steps to reproduce:
-------------------------
100% reproducible.
1. Launch a QEMU instance (No need websocket option):
qemu-system-x86_64 -enable-kvm -m 6G ./win_x64.qcow2 -vnc :0
2. Launch websockify on a separate host and connect to QEMU's VNC port
3. Open VNC Web Client (noVNC/vnc.html) in browser and connect to websockify
4. Play a video (e.g. Watch YouTube) on VM (To produce a lot of frame buffer update)
5. Limit (e.g. Use NetLimiter) the client inbound bandwidth to 300KB/S (To simulate a low speed WAN)
6. Then client's output gets stuck(less than 1 fps), the cursor is almost impossible to move
7. Monitor network traffic on the proxy server
Current result:
-------------------------
Monitor Downlink/Uplink network traffic on the proxy server
(Refer to the attachments for more details).
1. Used with QEMU
- D: 5.9 MB/s U: 5.7 MB/s (Client on LAN)
- D: 4.3 MB/s U: 334 KB/s (Client on WAN)
2. Used with other VNC servers
- D: 5.9 MB/s U: 5.6 MB/s (Client on LAN)
- D: 369 KB/s U: 328 KB/s (Client on WAN)
It is found that when the client's network is poor, all the VNC servers (tigervnc/x11vnc/tightvnc) will reduce the VNC data send to websocket proxy (uplink and downlink symmetry), but QEMU never drop any frames and still sends a lot of data to websockify, the client has no capacity to accept so much data, more and more data are accumulated in the websockify, then it crashes.
Expected results:
-------------------------
When the client's network is poor (WAN), QEMU will reduce the VNC data send to websocket proxy. |
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