Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ucsd!sdcsvax!darrell
From: preston@felix.uucp (Preston Bannister)
Newsgroups: comp.os.research
Subject: Re: Kernel Size
Message-ID: <4719@sdcsvax.UCSD.EDU>
Date: 6 Mar 88 00:17:21 GMT
Sender: darrell@sdcsvax.UCSD.EDU
Lines: 47
Approved: mod-os@sdcsvax.uucp


>From article <4702@sdcsvax.UCSD.EDU>, by mason@polya.stanford.edu :

> An interesting conjecture, that a small kernel equates with low efficiency,
> and a large kernel equates with high efficiency.  From what I've seen of the
> performance figures, this isn't truly supported.  For example, in V, ...

I was hoping someone from the V group would respond :-)

As you'll notice, Martin (large kernels :-) and I both work at
FileNet.  We have somewhat different viewpoints...

FileNet uses a modified version of Unix v7 (they started 5 years ago)
with the primary differences being a distributed filesystem, diskless
workstation support and a (unique:-) form of shared libraries.

The product that FileNet sells is a "document image processing system".  
We use an optical disk jukebox to store _massive_ amounts of documents.
The system is completed with scanners, laser printers, workstations
with high resolution displays and a fair amount of software.

Martin works in the operating system group (he just sped up the
filesystem).  I work on a part of the "application" software
(user-interface and a bit below).

From the inside our system is made up of a number of services
(document, index, print, and others) and application software that
makes use of those services.  

Our entire system is in the continuous process of evolution.  Services
are revised, enhanced or replaced fairly frequently.  While the OS is
a relatively small part of the overall system, in practice it is the
part that the most difficult to change.  Probably because it is the
largest _single_ piece.

I have difficulty with the assertion large kernels are more efficient.
In the real :-) world, smaller programs are easier to understand as a
whole, and therefore tend to evolve more rapidly.  Even if there is
some low-level advantage to throwing everything in the kernel, a it
seems likely that algorithmic improvements in smaller more rapidly
evolving software would soon more than make up for the difference.

--
Preston L. Bannister
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