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From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.protocols.nfs,comp.protocols.misc
Subject: Re: A Comparison of Commerical RPC Protocols
Summary: loopback / ethernet >> 0
Keywords: RPC Apollo Sun Netwise
Message-ID: <38963@sgi.SGI.COM>
Date: 27 Jul 89 01:33:01 GMT
References: <6567@joshua.athertn.Atherton.COM> <951@anise.acc.com> <44a7f591.1d6d5@apollo.COM>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 37

In article <44a7f591.1d6d5@apollo.COM>, mishkin@apollo.COM (Nathaniel Mishkin) writes:
> 
>  (about the RPC #'s)
>
> Some grains of salt:  The data reported in your paper was obtained by
> running client and server on the same machine.  I have to take a fair
> bit of exception with this.  I would imagine that the time to make a
> remote call is dominated (or at least significantly determined by) the
> networking costs (i.e. the cost of sending and receiving network messages).
> The cost of sending intra-machine network messages can be assumed to
> be roughly zero (relative to the inter-machine cost, anyway).  Your tests
> may thus have measured the relative speeds of things that are a small
> fraction of the total cost of making a remote call.
> -- 
>                     -- Nat Mishkin
>                        Apollo Computer Inc., Chelmsford, MA
>                        mishkin@apollo.com


ahem.

Ttcp measurements of raw user-to-user-space TCP and UDP over ethernet and
through the loopback drivers do show substantial differences, but much less
than 100%.  These measurements have been done on the presumably different
Sun Microsystems and Silicon Graphics systems (if they're identical,
someone's lawyers probably want to know :-).  Loopback could be expected to
save an interrupt, and maybe a byte copy or two if you're stuck with a bad
ethernet controller, but it does not affect the protocol code or number of
checksums or byte copies between network buffers and user space.

The big work is required or finessed regardless, and costs the same, unless
the ethernet hardware is helping.


Vernon Schryver
Silicon Graphics
vjs@sgi.com