Date: Mon, 28 Jun 1999 01:32:53 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Daniel J. O'Connor" <doconnor@gsoft.com.au> Cc: hackers@FreeBSD.ORG, Warner Losh <imp@harmony.village.org>, Julian Elischer <julian@whistle.com> Subject: Re: "restricted" kernel threads implementation from NetBSD via n Message-ID: <199906280832.BAA18397@apollo.backplane.com> References: <XFMail.990628173909.darius@dons.net.au>
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:I don't suppose someone could post an explanation of how kernel threads work
:could they? :)
:
:I sort of grasp the idea but I'm wondering what passes for context switches and
:stuff like that.. What does the switching between threads etc? Or am I
:completely off track?
:
:---
:Daniel O'Connor software and network engineer
Basically switching between kernel threads is the same as switching
between processes except that you do not need to mess with the MMU
or other complex scheduling elements, so switching between kernel threads
can be made almost as fast as a simple subroutine call.
A kernel thread can be thought of as a cheaper process. Threads are
often called "tasks". The terminology is the same, but still distinct
from "process".
This is key to being able to vector an interrupt to a kernel thread.
The interrupt code must already save much of the process context,
adding a little extra glue to turn it into a kernel thread that we
can actually switch-away from should theoretically be very cheap.
-Matt
Matthew Dillon
<dillon@backplane.com>
:for Genesis Software - http://www.gsoft.com.au
:"The nice thing about standards is that there
:are so many of them to choose from."
: -- Andrew Tanenbaum
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