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Re: [RFC] FPU context switch

To: Greg Lindahl <>
Subject: Re: [RFC] FPU context switch
From: Daniel Jacobowitz <>
Date: Tue, 17 Sep 2002 15:38:20 -0400
Cc: Jun Sun <>,
In-reply-to: <>
Original-recipient: rfc822;
References: <> <> <> <>
User-agent: Mutt/1.5.1i
On Tue, Sep 17, 2002 at 12:03:10PM -0700, Greg Lindahl wrote:
> On Tue, Sep 17, 2002 at 11:48:31AM -0700, Jun Sun wrote:
> > I think this gives a big performance improvement because most processes
> > don't use FPU during their runs but they all have used_math flag set!
> Jun,
> You really ought to prove that first. Many people spend a lot of time
> optimizing things that aren't important. If it isn't important, than
> the simplest scheme is the best choice.

Oh, he's quite correct.  There's a setjmp() early in the execution
path, and it saves FP registers on machines with FP support configured
on.  So tasks are marked as FPU users.

I've never thought of a terribly good way around this.

Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

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