From owner-cvs-all  Fri Nov  6 04:32:21 1998
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To: Matthew Dillon <dillon@apollo.backplane.com>
cc: Marc Slemko <marcs@znep.com>, cvs-committers@FreeBSD.ORG
Subject: Re: sendfile() 
In-reply-to: Your message of "Thu, 05 Nov 1998 23:23:59 PST."
             <199811060723.XAA01903@apollo.backplane.com> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Fri, 06 Nov 1998 04:33:29 -0800
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>    Heh.  Well, I wrote a little program to test the overhead of
>    sendfile() vs write() in the 100% cached case.  The program
>    makes a tcp connection to another program that just sinks the
>    data.
>
>    Over localhost (with the sink program running on the same
>    host), it's 9x more efficient to use sendfile().  Over
>    a 10BaseT Lan (with the sink program running on the
>    remote host) it's 2x and 2.8x more efficient using
>    sendfile().

   A couple of comments about the benchmarks: having a process on the same
machine sink the data will pessimize the results since there will be a
kernel->user copy, even though the data is thrown away. The LAN test you
did is unusually slow; on a P6/200 with 100Mbps DMA fast ether (fxp) talking
to another machine as a data sink, I measured very close to 1/10th of the CPU
consumption when sending a cached file vs. the same except using ttcp with a
cached file (which does a read/write loop).

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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