Date: Thu, 10 Jan 2002 13:52:17 -0800 From: Alfred Perlstein <bright@mu.org> To: Kelly Yancey <kbyanc@posi.net> Cc: Nate Williams <nate@yogotech.com>, 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>, arch@FreeBSD.ORG Subject: Re: Request for review: getcontext, setcontext, etc Message-ID: <20020110135217.M7984@elvis.mu.org> In-Reply-To: <Pine.BSF.4.21.0201101309200.6849-100000@gateway.posi.net>; from kbyanc@posi.net on Thu, Jan 10, 2002 at 01:14:05PM -0800 References: <15421.64170.308581.606485@caddis.yogotech.com> <Pine.BSF.4.21.0201101309200.6849-100000@gateway.posi.net>
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* Kelly Yancey <kbyanc@posi.net> [020110 13:14] wrote:
> 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.
> >
>
> 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)?
That's the point of this discussion, we're trying to figure out
why and if possible how to avoid them being system calls. :)
Basically what it seems to come down to are two points:
1) Is atomicity required? (looks like a "no")
2) Are states like FP usage trackable from userspace?
(looks like a "yes" with some kernel help)
--
-Alfred Perlstein [alfred@freebsd.org]
'Instead of asking why a piece of software is using "1970s technology,"
start asking why software is ignoring 30 years of accumulated wisdom.'
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