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From: chuck@ccrc.wustl.edu (Chuck Cranor)
Newsgroups: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc
Subject: Re: TCP latency
Followup-To: comp.os.linux.networking,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc
Date: 19 Jul 1996 11:18:03 -0500
Organization: Washington University, St. Louis MO
Lines: 42
Message-ID: <4socfr$3ot@dworkin.wustl.edu>
References: <4paedl$4bm@engnews2.Eng.Sun.COM> <4sadde$qsv@linux.cs.Helsinki.FI> <31E9E3A7.41C67EA6@dyson.iquest.net> <4sefde$f0l@fido.asd.sgi.com>
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Xref: euryale.cc.adfa.oz.au comp.os.linux.networking:45791 comp.unix.bsd.netbsd.misc:4117 comp.unix.bsd.freebsd.misc:23993
In article <4sefde$f0l@fido.asd.sgi.com>,
Larry McVoy <lm@slovax.engr.sgi.com> wrote:
>Umm, I'd be happy to entertain suggestions for a better measurement of
>a null entry into the system. I don't want something that anyone special
>cases - that's just worthless. I want something that is actually measuring
>all the work you need to do to get to the point that you can do something in
>the kernel.
I took Larry's lat_syscall.c and a few of J Wunsch's suggestion for
different system calls to try and ran a few tests. Here are the results:
[note: sparc 2 is running SunOS 4.1.3_U1 (48MB RAM), P5-133MHz is running
NetBSD/i386 (32MB RAM) ... both systems unloaded. all numbers are
microseconds]
program description Sparc2 P5-133MHz
lat_syscall write 1 to /dev/null 61 6
lat_gettime gettimeofday(&tv,0) 27 5
lat_kill kill(1,0) 23 2
lat_umask umask(0) 19 2
lat_getppid getppid() 17 1
Given that data, it seems like lat_syscall's writing 1 byte to /dev/null
is indeed a poor measurement of "Null syscall." This leaves me with
two questions:
1. Larry, when you were designing lat_syscall, did you see numbers like
the above? If not, then I would consider that a mistake. If so,
then why did you stick with "write 1 to /dev/null" as a measurement
of "Null syscall" (which I also consider a mistake)?
2. How much of the difference between FreeBSD lat_syscall and Linux
lat_syscall can be attributed to VFS overhead in FreeBSD? Or
more generally, how does the overhead and functionality of Linux's
VFS layer compare with FreeBSD's VFS layer?
chuck
--
>>Chuck Cranor, Graduate Student, Computer and Communications Research Center<<
>>Washington University, St. Louis MO http://www.ccrc.wustl.edu/pub/chuck <<
... help! my wife has accepted a job with at&t research in new jersey and
now i've got to find a job in new jersey too ...