[RFC] simulating network properties for benchmarks

[Robert Collins]

On Thu, 2006-07-20 at 23:08 +0200, Carl Friedrich Bolz wrote:
> 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.


Heres a prototype of what I was referring to. The decorator in it was
quick-coded, if the future directions I mention in it are to be done, it
would deserve unit tests, as high layer tests could no longer test it at
that point.

I'm pushing this up to
sftp://bazaar.launchpad.net/~bzr/bzr/test-sftp-latency now.

Cheers,
Rob

-- 
GPG key available at: <http://www.robertcollins.net/keys.txt>.
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