Subject: RE: Kernel Threads (was Floating point in the kernel)
To: 'John F. Woods' <>
From: Calvin Vette (IT- Borders Online) <>
List: tech-kern
Date: 09/18/1998 15:19:51
	The URL below describes a system similar to Sun's lwp, but
asynchronous - a combined kernel/user thread mechanism. Is this along the
lines of what you have in mind?

	From:  John F. Woods []
	Sent:  Friday, September 18, 1998 1:52 PM
	Cc:  Jason Thorpe; John F. Woods;
	Subject:  Re: Floating point in the kernel 

	> I believe that the notion was that one day that might be 'fixed.'
	> But, because there are lots of them and they may switch often, you
	> really want kernel thread switching ot be as lightweight as
	> possible...  So i still think it's unlikely.

	And (as I was going to point out in a message eaten by a PPP line
	once you *have* kernel threads, you find that they're the answer to
	about every kernel programming problem, so (as you said) you want
them to
	be as lightweight as possible.

	But I hope that threads (user threads, anyway) will not be made
	lightweight:  if the kernel is aware of user threads and schedules
	(as opposed to threads existing as figments of user processes'
	then (a) you get non-blocking I/O for "free" (one thread blocking in
	doesn't block other threads in that process), and (b) different
threads of
	a process can make use of multiple CPUs (OK, so that's more
interesting on
	a 256 processor KSR machine than in is on a dual-Pentium... ;-) ).
	makes threads heavier-weight than one might like (and, worse, leads
	people searching for new terms like "fibers" for threads that exist
	figments of a thread's imagination... ;-) ), but it makes threads
just so
	much more useful.