Re: [openflowplugin-dev]

Anton Ivanov

On 30/03/15 09:12, Michal Polkoráb wrote:

Hi Anton,

do we have any performance numbers (to compare with original code performance) ?

This one - not yet. I started setting up a benchmark environment as I have to do proper benchmarks for the proposed fixes for ser/des as well (bug 2825) last week.

Unfortunately, I had to switch urgently to clear something else out of my queue. I am just about done with what I had to context-switch to, so I will get back to the benchmark task ASAP.

Otherwise, I have worked on similar stuff in the past - the difference depends on rtt.

Based on my recollections from implementing mobile signalling over TCP, for very small rtt (virtual switch on same host) it will probably be not more than 50% for command-acknowledge sequence. For LAN you are looking at 2x difference. For WAN - even more than that. For ~ 10ms you may see several times difference depending on use case.

There is a reasonable write-up on this here:

Java does not do cork, but we can emulate it in the ser/des layer so that is not a big deal.

Further write up here

and ... frankly everywhere. All the way back to TCP Illustrated.

This is the de-facto standard of implementing low-latency TCP response-ack. If you do not do it, you are guaranteed to get the latencies which the world is demonstrating for our stuff on CBENCH.



Michal Polkorab

From: Edward Warnicke <hagbard@...>
Sent: 27 March 2015 12:25
To: Anton Ivanov; openflowjava-dev
Cc: openflowplugin-dev@...
Subject: Re: [openflowjava-dev] [openflowplugin-dev]
Looping in openflowjava-dev, where this patch is actually applied.


On Fri, Mar 27, 2015 at 4:29 AM, Anton Ivanov <anton.ivanov@...> wrote:
Looks like jenkins is out with the daisies. Again :)

It is not even starting build jobs at the moment.

In any case, Abhjit, Michal, please review - this one is obvious.

We never have "throughput" in the sense TCP as a protocol puts into it. What we have is more of a NO_DELAY scenario.

Additionally, once this has been fixed, there are a couple of other netty tunables (specifically rexmit attempts) which need to be revisited. Hitting a retransmit in a NO_DELAY scenario is a clear indication of an error or waiting for a TCP retransmission of an ACK from peer. In that case using the "beatings will continue until the morale improves" approach regarding the TCP stack is useless. It does not matter how many time you resubmit it will not transmit. It just wastes a mass of CPU which could have been used to service other sockets in the netty pool.

I will file that (and submit a patch) once we have finished this one off.

There are some other additional issues on Linux related to cork, autocork, etc, but they cannot be dealt with in Java as it does not do OS specific TCP options. So there is no way to solve them from inside ODL.

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