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Xref: sserve comp.os.386bsd.questions:12307 comp.os.386bsd.misc:3173 Newsgroups: comp.os.386bsd.questions,comp.os.386bsd.misc Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!bunyip.cc.uq.oz.au!munnari.oz.au!constellation!mimbres.cs.unm.edu!tesuque.cs.sandia.gov!lynx.unm.edu!nntp.sunbelt.net!udel!gatech!howland.reston.ans.net!agate!library.ucla.edu!csulb.edu!csus.edu!netcom.com!netcomsv!calcite!vjs From: vjs@calcite.rhyolite.com (Vernon Schryver) Subject: Re: Whats wrong with Linux networking ??? Message-ID: <CuBoHD.AEE@calcite.rhyolite.com> Organization: Rhyolite Software Date: Wed, 10 Aug 1994 14:05:37 GMT References: <327nj0$sfq@sundog.tiac.net> <328fn2$i9p@news.panix.com> <32920b$m5n@orion.cc.andrews.edu> Lines: 27 In article <32920b$m5n@orion.cc.andrews.edu> gillham@andrews.edu (Andrew Gillham) writes: >>Could you explain why this should be the case? Since 8K blocks will typically >>(eg. on an Ethernet) be fragmented by IP down to ~1K packets, why should these >>bigger blocks be an advantage. If anything I would suspect that >>reassembly and retransmission costs would make the <MTU packets better. > >I would say the difference is the 'layers' that are involved. >At what layer in the OS is the IP packet fragged versus at what layer >is a 1k NFS read taking place? How many system calls or context >switches are involved in making a NFS write call? (both ends) >Seems to me that if the upper layer asks to write 8k, jumps through >the system call hoops to get to the IP transmit layer, it only does that >once for 8k, instead of around 5 times. Then the IP layer fragments it >and sends it. Someone else would have to comment on whether it can send >the fragmented (to ~1500 bytes?) without context switching or making >many system calls. Also I would imagine there is connection info, etc >that each nfs write packet would duplicate. I don't know about Linux, but in 4.*BSD TCP/IP (including SVR3 and SVR4.0), IP fragmentation is done in one bash as the NFS/UDP packet is passed through IP. As I recall, in the old Sun NFS code, NFS itself IP fragmented and then called the output hooks of the drivers directly. Layering is not an issue. Vernon Schryver vjs@rhyolite.com