Somebody in the Zoom call the other day (IIRC it was Gernot) said that
seL4 IPC is considerably faster than QNX IPC, but it seems that QNX is
somehow faster in a simple benchmarking experiment in which a client
repeatedly sends messages to a bit-bucket server, using the TSC to
determine timing.
I'm running both QNX and seL4 under identical VirtualBox
configurations with a single core. I'm using a QNX 6.3.1 x86-32 image
i have in my collection (x86-64 support was only added in 7.0; this is
the most recent image I have with dev tools installed). The seL4
version I'm using is from February 2022 and is built for x86-64 with
MCS enabled (the priority of the threads is 255, and both the
timeslice and budget are the initial thread default of 5 ms).
My benchmark times a loop of 10000 RPCs; for QNX it's just using the
regular read() function on /dev/null or a custom server that also acts
like /dev/null but forces a copy of the message into a server-provided
buffer, and for seL4 I'm directly calling Send()/Recv()/Reply(). I've
also tested Linux's /dev/null, and QNX's implementation actually seems
somewhat faster than it (for the system /dev/null; the custom server's
best case seems only slightly worse than under Linux).
Under QNX and Linux I'm running a C implementation of the benchmark
and under seL4 I tried both C and Rust implementations (which have
very similar performance). The messages on QNX and Linux are 100
bytes, and on seL4 they are 2 words, which should be hitting the fast
path.
Here are the best and worst cases I got:
seL4: 0.114-0.136s
QNX, custom null server: 0.006-0.063s
QNX, system null server: 0.002-0.022s
Linux: 0.004-0.005s
Has anyone else benchmarked seL4 IPC against that of QNX and gotten
better (or comparable) results for seL4, unlike what I got? Is
synchronous IPC just less optimized under seL4 than QNX?
