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From: dillon@flea.best.net (Matt Dillon)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: dd `benchmark'
Date: 5 Jul 1997 12:32:39 -0700
Organization: Best Internet Communications, Inc. - 415 964 BEST
Lines: 51
Message-ID: <5pm7gn$ds6$1@flea.best.net>
References: <u7wwn5jrs0.fsf_-_@japonica.csl.sri.com>
NNTP-Posting-Host: flea.best.net
Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:43993
:In article <u7wwn5jrs0.fsf_-_@japonica.csl.sri.com>,
:Fred Gilham <gilham@japonica.csl.sri.com> wrote:
:>
:>A few people have posted messages talking about doing
:>
:>dd if=/dev/zero of=/dev/null bs=1m count=1000
:>
:>as a memory system benchmark. I'm very curious if anyone knows
:>exactly what this measures. The reason is that I have results I find
:>curious.
:..
:>--
:>-Fred Gilham gilham@csl.sri.com
Basically all this measures is the size of your cache, which you
know anyway:
apollo:/root# dd if=/dev/zero of=/dev/null bs=1024k count=1000
1000+0 records in
1000+0 records out
1048576000 bytes transferred in 16.018573 secs (65460013 bytes/sec)
apollo:/root# dd if=/dev/zero of=/dev/null bs=512k count=2000
2000+0 records in
2000+0 records out
1048576000 bytes transferred in 16.256316 secs (64502683 bytes/sec)
apollo:/root# dd if=/dev/zero of=/dev/null bs=256k count=4000
4000+0 records in
4000+0 records out
1048576000 bytes transferred in 4.419116 secs (237281851 bytes/sec)
apollo:/root# dd if=/dev/zero of=/dev/null bs=128k count=8000
8000+0 records in
8000+0 records out
1048576000 bytes transferred in 3.631254 secs (288764160 bytes/sec)
apollo:/root# dd if=/dev/zero of=/dev/null bs=64k count=16000
16000+0 records in
16000+0 records out
1048576000 bytes transferred in 3.724366 secs (281544827 bytes/sec)
Gee, guess that means I have a 256K cache in my PPro 200 running
FreeBSD.
Nor are the numbers between operating systems very meaningful...
it depends how they implement /dev/zero and /dev/null which, in most
cases, is irrelevant to the operation of the rest of the system.
-Matt