[Bug 1725707] Re: QEMU sends excess VNC data to websockify even when network is poor

[Thomas Huth]

The QEMU project is currently considering to move its bug tracking to another 
system. For this we need to know which bugs are still valid and which could be 
closed already. Thus we are setting older bugs to "Incomplete" now.
If you still think this bug report here is valid, then please switch the state 
back to "New" within the next 60 days, otherwise this report will be marked as 
"Expired". Or mark it as "Fix Released" if the problem has been solved with a 
newer version of QEMU already. Thank you and sorry for the inconvenience.


** Changed in: qemu
       Status: New => Incomplete

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Title:
  QEMU sends excess VNC data to websockify even when network is poor

Status in QEMU:
  Incomplete

Bug 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.

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