Date: Mon, 14 Jan 2002 08:53:30 +1100 From: Peter Jeremy <peter.jeremy@alcatel.com.au> To: Alfred Perlstein <bright@mu.org> Cc: Kelly Yancey <kbyanc@posi.net>, 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: <20020114085330.B38605@cirb503493.alcatel.com.au> In-Reply-To: <20020110135217.M7984@elvis.mu.org>; from bright@mu.org on Thu, Jan 10, 2002 at 01:52:17PM -0800 References: <15421.64170.308581.606485@caddis.yogotech.com> <Pine.BSF.4.21.0201101309200.6849-100000@gateway.posi.net> <20020110135217.M7984@elvis.mu.org>
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On Thu, Jan 10, 2002 at 01:52:17PM -0800, Alfred Perlstein wrote:
>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)
I gather you are thinking of a userland approach like:
if (thread_has_used_FP) {
save_FP_context(curthread);
mark_FP_unused();
}
save_nonFP_context(curthread);
restore_nonFP_context(newthread);
if (FP_is_used(newthread))
pass_FP_context_to_kernel(newthread);
curthread = newthread;
Since FP status is per-CPU, this needs atomicity to an
extent: You must ensure that the active thread does not
migrate between CPUs between the "thread_has_used_FP" test
and following save. I agree this is unlikely, but it needs
to be catered for.
Peter
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