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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.mira.net.au!news.vbc.net!samba.rahul.net!rahul.net!a2i!olivea!sgigate.sgi.com!swrinde!howland.reston.ans.net!Germany.EU.net!Dortmund.Germany.EU.net!interface-business.de!usenet From: j@ida.interface-business.de (J Wunsch) Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc Subject: Re: TCP latency Date: 11 Jul 1996 14:39:15 GMT Organization: interface business GmbH, Dresden Lines: 41 Message-ID: <4s33mj$fv2@innocence.interface-business.de> References: <4paedl$4bm@engnews2.eng.sun.com> <31DC8EBA.41C67EA6@dyson.iquest.net> <4rlf6i$c5f@linux.cs.helsinki.fi> <31DEA3A3.41C67EA6@dyson.iquest.net> <Du681x.2Gy@kroete2.freinet.de> <31DFEB02.41C67EA6@dyson.iquest.net> <4rpdtn$30b@symiserver2.symantec.com> <x7ohlq78wt.fsf@oberon.di.fc.ul.pt> <Pine.LNX.3.91.960709020017.19115I-100000@reflections.mindspring.com> <x74tnfn35s.fsf@oberon.di.fc.ul.pt> Reply-To: joerg_wunsch@interface-business.de (Joerg Wunsch) NNTP-Posting-Host: ida.interface-business.de X-Newsreader: knews 0.9.6 X-Phone: +49-351-31809-14 X-Fax: +49-351-3361187 X-PGP-Fingerprint: DC 47 E6 E4 FF A6 E9 8F 93 21 E0 7D F9 12 D6 4E Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:44797 comp.unix.bsd.netbsd.misc:3996 comp.unix.bsd.freebsd.misc:23302 Pedro Roque Marques <roque@di.fc.ul.pt> wrote: > Like i mentioned in a > previous post BSD style timers tend to be cheaper but they are less > correct than what one would normally desire. One of the finest remarks > i've heard on this issue was "if most of the times the retransmit > timer won't expire, why set it in the first place ?" the tought part > is that when the timer expires with want it to expire with the greatest > precision you can achieve. Sorry for my ignorance, network code is arguably not my field of knowledge. What's the (user-visible) drawback of the current scheme? I do know that the BSD TCP code sometimes suffers from poor recovery behaviour on lossy lines (packet loss >~ 50 %, as it can often be observed on transatlantic or transpacific links). Is this what you mean? > - As for the routing table maintainance/lookup, i'm not familiar > enough with it but i think that in 2.0 Linux has a resonably good/fast > code. Rumor is that the big plans are to support part of the routing table in > user space (which has the great advantage of being swapable). I think this is the wrong approach. The IMHO correct approach is to allow the kernel code to declare parts of it as pageable. I know at least one system (DG/UX) that allows for this (each kernel object is declared either `wired' or `unwired'). Besides this (i know about the same of the Linux kernel as you know of the FreeBSD network system :), can't you already allocate the space for your routing table in pageable memory? In FreeBSD, i can explicitly demand to get pageable (dynamic) memory. The only thing that is currently impossible (and will remain impossible as long as we use a.out for the kernel) is to allow for pageable non-dynamic objects (i.e., everything that comes directly from the C source). Anyway, i'm afraid a pageable routing table might cause a lousy network performance in case of memory tightness. -- J"org Wunsch Unix support engineer joerg_wunsch@interface-business.de http://www.interface-business.de/~j