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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!nntp.coast.net!news.kei.com!news.mathworks.com!tank.news.pipex.net!pipex!usenet2.news.uk.psi.net!uknet!usenet1.news.uk.psi.net!uknet!uknet!news.swan.ac.uk!iialan From: iialan@iifeak.swan.ac.uk (Alan Cox) Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc Subject: Re: TCP latency Date: 16 Jul 1996 08:37:55 GMT Organization: Institute For Industrial Information Technology Lines: 29 Message-ID: <4sfkd3$a11@news.swan.ac.uk> References: <31E7C0DD.41C67EA6@dyson.iquest.net> <4s8tcn$jsh@fido.asd.sgi.com> <31E80ACA.167EB0E7@dyson.iquest.net> NNTP-Posting-Host: iifeak.swan.ac.uk Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:45380 comp.unix.bsd.netbsd.misc:4071 comp.unix.bsd.freebsd.misc:23714 In article <31E80ACA.167EB0E7@dyson.iquest.net> "John S. Dyson" <toor@dyson.iquest.net> writes: >I think that was a kind-of cute situation. We decided NOT >to special case the syscall that Larry uses for the >null-syscall case. Nor does Linux. Its just fast at syscalls. Reminds me Linus, it looks like there are about 3 clocks you can save on syscall entry by changing the handling of a syscall slot containing zero. In terms of the benchmark however Larry ought to use getppid() which cannot be cached (you may get inherited by init). You could conceivably mmap the page containing ppid info into the program but thats just grotesque ;) Also a couple of people have been muttering things about code layout and TLB misses. On a pentium the Linux kernel except when accessing user space and on kernel entry doesnt take TLB misses. Cache footprints however are a big issue (for example the Linux lat_tcp throughput figures double on some machines if you do ifconfig lo mtu 1500 - as far as I can tell because it then all fits nicely in L1 cache). PC's are horrible varied pieces of equipment and I've seen motherboards with the same chipset and a factor of two memory performance difference, so as various people have said - all benchmarks have to be done on the same kit. Alan -- Send unsolicited junk mail to this address and maybe win the chance to have yourself added free to several hundred random mailing lists. ,--------------- ------------------------------------------------------------/ Alan Cox This signature comes with a free redistribution license / alan@cymru.net