Messages in this thread | | | Date | Thu, 29 Oct 2009 16:19:33 +0100 | Subject | Re: [PATCH 2/3] net: TCP thin linear timeouts | From | apetlund@simula ... |
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I apologise that some of you received this mail more than once. My email client played a HTML-trick on me.
> Eric Dumazet schrieb: >> Andreas Petlund a écrit : >>> This patch will make TCP use only linear timeouts if the stream is thin. This will help to avoid the very high latencies that thin stream suffer because of exponential backoff. This mechanism is only active if >>> enabled by iocontrol or syscontrol and the stream is identified as thin. >> Wont this reduce the session timeout to something very small, ie 15 retransmits, way under the minute ? > > The session timeout no longer depends on the actual number of retransmits. > Instead its a time interval, > which is roughly equivalent to the time a TCP, performing exponential backoff would need to perform > 15 retransmits. > > However, addressing the proposal: > I wonder how one can seriously suggest to just skip congestion response during timeout-based > loss recovery? I believe that in a heavily congested scenarios, this would > lead to a goodput > goodput disaster... Not to mention that in a heavily congested scenario, suddenly every flow > will become "thin", so this will even amplify the problems. Or did I miss > something?
We have found no noticeable degradation of the goodput in a series of experiments we have performed in order to map the effects of the modifications. Furthermore, the modifications implemented in the patches are explicitly enabled only for applications where the developer knows that streams will be thin, thus only a small subset of the streams will apply the modifications.
Graphs presenting results from experiments performed to analyse latency and fairness issues can be found here: http://folk.uio.no/apetlund/lktmp/
-AP
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