linux-mips
[Top] [All Lists]

Re: [RFC] FPU context switch

To: Greg Lindahl <lindahl@keyresearch.com>
Subject: Re: [RFC] FPU context switch
From: Daniel Jacobowitz <dan@debian.org>
Date: Tue, 17 Sep 2002 15:38:20 -0400
Cc: Jun Sun <jsun@mvista.com>, linux-mips@linux-mips.org
In-reply-to: <20020917120310.A2043@wumpus.internal.keyresearch.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20020917110423.E17321@mvista.com> <1032288140.28433.165.camel@gs256.sp.cs.cmu.edu> <20020917114831.G17321@mvista.com> <20020917120310.A2043@wumpus.internal.keyresearch.com>
Sender: linux-mips-bounce@linux-mips.org
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

<Prev in Thread] Current Thread [Next in Thread>