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From: peter@nmti.com (Peter da Silva)
Newsgroups: comp.os.linux.misc,comp.os.linux.networking,comp.os.linux.setup,comp.unix.bsd.bsdi.misc,comp.unix.bsd.misc
Subject: Re: User-space file systems. (Re: Linux vs BSD)
Date: 5 Mar 1997 15:01:53 GMT
Organization: Network/development platform support, NMTI
Lines: 34
Message-ID: <5fk1t1$3mq@web.nmti.com>
References: <5e6qd5$ivq@cynic.portal.ca> <5f283t$667@cynic.portal.ca> <5fj9q4$s0i@pulp.ucs.ualberta.ca> <5fjek4$gtm@cynic.portal.ca>
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In article <5fjek4$gtm@cynic.portal.ca>,
Curt Sampson <cjs@cynic.portal.ca> wrote:
> I don't see any way to avoid crossing the user/kernel boundaries
> any fewer number of times unless you move the NFS daemon into the
> kernel, or move either the disk I/O or the networking (or both)
> into userland. The latter is obviously not terribly practical,
> except perhaps for a dedicated NFS serving machine.
But, Curt, reading a *local* disk block makes two kernel transitions anyway.
Reading a disk block over NFS, from the *client*, costs that plus network
latency. You'd speed up NFS far more with client side caching. You're looking
at a few percent of the total time (real time AND CPU time) cost of a
transaction here.
Yes, moving NFS into the kernel is a Good Thing, but it's not obvious to
me that it's enough of a Good Thing to make it such a big issue.
And userland file systems are themselves a really nifty tool. Look at things
like Alex for an example. Wouldn't it be nice to be able to run Alex *and*
regular NFS at the same time on the same server?
Things like that are much more easily implemented when you have a userland
file system.
Look at it this way... I used a microkernel type operating system for years,
on my Amiga. The most common tool that was implemented there of all the things
a microkernel could do that a monolithic kernel can't, was new kinds of file
systems. If you can do userland file systems you get 95% of what people want
microkernels for anyway.
--
The Reverend Peter da Silva, ULC, COQO, BOFH.
Har du kramat din varg, idag? `-_-'