Date: Thu, 4 Feb 1999 08:50:42 -0600 From: Guy Helmer <ghelmer@scl.ameslab.gov> To: "Dirk-Willem van Gulik (vaio)" <dirkx@webweaving.org> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Irratic Curve Message-ID: <Pine.SGI.4.05.9902040836570.2662-100000@demios.scl.ameslab.gov> In-Reply-To: <36B97B38.74FF0B68@webweaving.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, 4 Feb 1999, Dirk-Willem van Gulik (vaio) wrote: > Whilst playing with a small, but fast, berkely DB based transaction > server; which sits on a tcp/ip socket connection I ran into sometimes > unpredictable reply times. One of the major problem was solved by > increasing the MSIZE to 256 (the 103 bytes+ delayed ack problem). A performance fix for message sizes around 100 bytes was committed and will appear in the 3.1 release. > Now recently I came across: > > http://www.scl.ameslab.gov/Projects/Gigabit/performance/prelim.html > > Now could any one explain to me WHY freebsd appears so unpredicatable ? > i.e. not a nice S-curve ? Is that the way of measuring ? Some other > artifact, or real ? I think it is real, as I get the same sort of > holes in my graphs for the transaction server. Well, if you look at figure 3 on that page, it shows how changing the TCP stack to not use delayed acknowledgements eliminates the dropouts (I noticed that the change to the TCP stack is not explained on the page you reference, but it is briefly mentioned at http://www.scl.ameslab.gov/Publications/Gigabit/tr5126.html). You can take advantage of a similar change to the FreeBSD TCP stack in versions 3.0 and later by doing "sysctl -w net.inet.tcp.delayed_ack=0" to turn off delayed acknowledgements. I believe this results in non-RFC-compliant behavior (I'm sure someone more familiar with the standard RFCs will correct me if I'm wrong), but it does improve performance dramatically in some circumstances. Guy Guy Helmer, Ph.D. Candidate, Iowa State University Dept. of Computer Science Research Assistant, Ames Laboratory --- ghelmer@scl.ameslab.gov Research Assistant, Dept. of Computer Science --- ghelmer@cs.iastate.edu http://www.cs.iastate.edu/~ghelmer To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.SGI.4.05.9902040836570.2662-100000>