The Design and Implementation of the Anykernel and Rump Kernels

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The results are presented in Figure 4.19. Rump kernels perform second best in the
test after User Mode Linux. However, the figures are not directly comparable due
to different hosts.
All virtualization technologies perform significantly worse than the native case. This
performance drop is because pinging a local address allows the system to route the
packet through the loopback address. Since a virtualized OS does not have a local
address configured on the host, the packet must be transmitted to the virtual OS
instance and back.
4.6.7 Web Servers
A web server performance test provides a macro benchmark of the performance of
the TCP/IP stack in a rump kernel. We tested by adapting the thttpd [7] web
server as a local client for a rump kernel. We used ApacheBench to measure the
total execution time for 10,000 requests of an 80 byte root document on the web
server. ApacheBench is always running against the host kernel TCP/IP stack, while
the web server was run both against the host stack and the virtual stack. The rump
kernel uses the virt interface, so as to access the host network. The results are
displayed in Figure 4.20.
With concurrency of 4 and above, the difference is about 0.1s in total time. The
figure translates to a 0.01ms (3%) difference per request. We attribute this difference
to the fact that in addition to the normal interface path, the rump kernel setup must
deliver packets through the tap and bridge drivers. We did not attempt to optimize
the host for Ethernet access to be available from userspace more directly.
While the above is most likely an obvious result, there are more delicate implications.
Running ApacheBench put 10,000 connections in TIME_WAIT on the server. This