[RFC] simulating network properties for benchmarks

[Carl Friedrich Bolz]

Hi all!

This mail is trying to start a discussion about various approaches on
how to test different network properties (latency, bandwidth, dns
latency, etc). The test should be repeatable, somewhat easily doable
(e.g. not involving a huge setup) and realistic.

During the performance-sync meeting we discussed briefly two general
approaches for this:

 * Using a proxy/decorator for a transport that adds some sort of
   artificial overhead to every operation, like time.sleep or similar.
   This has the advantage of being relatively easy to implement but the
   disadvantage of being quite unrealistic, since the operations on the
   transport don't really map in a straightforward manner to what is
   going on at packet level.

 * Simulating network properties on a lower level. If done right, this
   would be quite realistic. It may be harder to implement (but Robert
   hinted that he might have some ideas how to do it easily). The
   only somewhat simple idea I have currently is using netem
   (see http://linux-net.osdl.org/index.php/Netem) to slow down network
   operations. Works only under Linux and some care has to be taken to
   get it right.

Thoughts?

Cheers,

Carl Friedrich