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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.ecn.uoknor.edu!news.wildstar.net!newsfeed.direct.ca!nntp.portal.ca!news.bc.net!rover.ucs.ualberta.ca!gpu4.srv.ualberta.ca!not-for-mail From: jgg@gpu4.srv.ualberta.ca (E Runeland) Newsgroups: comp.os.linux.misc,comp.os.linux.networking,comp.os.linux.setup,comp.unix.bsd.bsdi.misc,comp.unix.bsd.misc Subject: Re: User-space file systems. (Re: Linux vs BSD) Followup-To: comp.os.linux.misc,comp.os.linux.networking,comp.os.linux.setup,comp.unix.bsd.bsdi.misc,comp.unix.bsd.misc Date: 5 Mar 1997 08:10:44 GMT Organization: University of Alberta Lines: 30 Message-ID: <5fj9q4$s0i@pulp.ucs.ualberta.ca> References: <5e6qd5$ivq@cynic.portal.ca> <stephenkE62DGo.6J5@netcom.com> <5etj32$3kh@cynic.portal.ca> <5evsnm$1200@usenet1y.prodigy.net> <5f283t$667@cynic.portal.ca> NNTP-Posting-Host: gpu4.srv.ualberta.ca X-Newsreader: TIN [UNIX 1.3 950824BETA PL0] Xref: euryale.cc.adfa.oz.au comp.os.linux.misc:162774 comp.os.linux.networking:70865 comp.os.linux.setup:100963 comp.unix.bsd.bsdi.misc:6202 comp.unix.bsd.misc:2712 Curt Sampson (cjs@cynic.portal.ca) wrote: : In article <5evsnm$1200@usenet1y.prodigy.net>, : bill davidsen <davidsen@tmr.com> wrote: : : A protection switch occurs every time data crosses the kernel-userland : boundary. In this case, that means approximately four protection : switches for every NFS packet. It doesn't matter how much CPU you're : using; the protection switches are slow and expensive. In fact, : the less CPU you use the worse the problem looks, since that : protection switch becomes a much greater proportion of the cost of : running the daemon, and moving it into the kernel will save all : that much more. I think this discussion is quite interesting, but one point that no-one has brought up is quite simply, why does linux have such a slow protection switch time? Instead of saying that NFS in userland is too slow because it needs to do 4 switches per packet and each switch is horribly slow, therefore it should be moved into kernel-space, why not say, linux's protection switch code could be optimized so that NFS is faster? Or perhaps even, how can we optimize the kernel calls so that only 1 per packet is required? Just moving the whole daemon into the kernel is a solution to speed problems, but by that same token other deamons that are 'performace critical' (http, ftp etc) should be moved into the kernel and you end up with a monolithic bloatware kernel :< If you ask me, moving stuff into the kernel is really only a band-aid patch for the real problem of high user-user and user-kernel switch times. Jason