From owner-freebsd-arch  Thu Jan 10 13:14:11 2002
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Date: Thu, 10 Jan 2002 13:14:05 -0800 (PST)
From: Kelly Yancey <kbyanc@posi.net>
To: Nate Williams <nate@yogotech.com>
Cc: Terry Lambert <tlambert2@mindspring.com>,
	Daniel Eischen <eischen@pcnet1.pcnet.com>,
	Dan Eischen <eischen@vigrid.com>, Peter Wemm <peter@wemm.org>,
	Archie Cobbs <archie@dellroad.org>, Alfred Perlstein <bright@mu.org>,
	arch@FreeBSD.ORG
Subject: Re: Request for review: getcontext, setcontext, etc
In-Reply-To: <15421.64170.308581.606485@caddis.yogotech.com>
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On Thu, 10 Jan 2002, Nate Williams wrote:

> See above.  Even in 5.0, we're going to have some threads being switched
> in userland context, while others are switched in the kernel.  (KSE is a
> hybrid approach that attempts to gain both the effeciency of userland
> threads with the ability to parallelize the effeciency gains of multiple
> CPU && I/O processing from kernel threads.
> 
> Nate
> 

  OK, I'm going to stick my head in and show my ignorance. If {get,set}context
have to be implemented as system calls, then doesn't that eliminate much, if
not all, the gains assumed by having a separate userland scheduler? I mean if
we've got to go to the kernel to switch thread contexts, why not just have the
kernel track all of the threads and restore context once, just for the current
thread, rather than twice (once for the scheduler and another for the
scheduler to switch to the current thread context)?

  Kelly


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