[48055] in North American Network Operators' Group
Re: Linux routing
daemon@ATHENA.MIT.EDU (Valdis.Kletnieks@vt.edu)
Wed May 22 09:21:22 2002
Message-Id: <200205221320.g4MDKgsp002807@turing-police.cc.vt.edu>
To: Peter van Dijk <peter@dataloss.nl>
Cc: nanog@merit.edu
In-Reply-To: Your message of "Wed, 22 May 2002 09:45:46 +0200."
<20020522074545.GA51074@dataloss.nl>
From: Valdis.Kletnieks@vt.edu
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Date: Wed, 22 May 2002 09:20:41 -0400
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On Wed, 22 May 2002 09:45:46 +0200, Peter van Dijk <peter@dataloss.nl> said:
> Why are you benchmarking network troughput by bzip2'ing a file in
> /tmp? It makes no sense.
I'm suspecting that he's trying to indirectly measure the kernel CPU usage.
Most kernels don't give you the time spent in kernel mode (or bill
it incorrectly to a process - I seem to remember some handwaving in either
the Keifler&McKusic or Bach books about how interrupt time is charged against
the current process, but it usually evens out in the end). So what you end
up doing is running a cycle-sucking CPU-bound process, and seeing how much
progress it makes - if in 60 seconds, the cycle sucker gets 45, then your
kernel is getting the other 25% (or so the theory goes).
It's not perfect, but it works as a back-of-envelope test and is probably
accurate to within 5-10%...
--
Valdis Kletnieks
Computer Systems Senior Engineer
Virginia Tech
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