simple IPC test results

[Norman Feske]

Hello,

On 03.04.2018 05:00, yu000013 wrote:
> Then I modified etc/build.conf to enable kvm...
...> That is, the cycles elapsing while executing ONE Rpc_add would be
around
> 8000 to 17000 cycles, which seems very long.
> 
> So I want to know: is these results reasonable? Or I missed anything in
> my tests?

your intuition is right. The numbers are certainly skewed by running
Genode in a virtual machine. To get reasonable numbers, you'll need to
execute the benchmark on real hardware.

May I ask about the motivation behind these measurements? I fear that
you may mistake the outcome of microbenchmarks to draw generalized
conclusions like kernel X is faster than kernel Y. In real-world
scenarios, performance is influenced by many other factors than IPC
roundtrip times, like cache/TLB footprint, platform setup (clocks,
caching, use of MSIs), scheduling, or the friction between the kernel
interface and the user space. To give an example for the latter,
traditional L4 kernels lack a mechanism for asynchronous notifications.
On these kernels, Genode's signaling API is implemented by using
synchronous IPC and the core component as a proxy service. Even though
synchronous IPC is fast, asynchronous notifications have to carry a lot
of overhead.

I encourage you to take your measurements at a higher level to attain
meaningful information out of your work. Possible examples are the
throughput and latency of the NIC session interface, latency of ROM
session updates, IRQ session latency, duration of component startup,
framebuffer access, timer accuracy, or the latency of delivering user
input events. As Genode is a component-based system, the chaining of
components is particularly interesting, e.g., how does the network
performance suffer from piping the traffic through a number of
bump-in-the-wire network-processing components?

Once one finds an interesting anomaly, a specially crafted
microbenchmark that artificially magnifies the issue would be the right
tool to pinpoint the problem.

Cheers
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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