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Re: FPU emulator unsafe for SMP?

To: Florian Lohoff <flo@rfc822.org>
Subject: Re: FPU emulator unsafe for SMP?
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Wed, 20 Feb 2002 14:56:49 +0100
Cc: Dominic Sweetman <dom@algor.co.uk>, Jun Sun <jsun@mvista.com>, "Kevin D. Kissell" <kevink@mips.com>, linux-mips@oss.sgi.com
In-reply-to: <20020220093012.GF11654@paradigm.rfc822.org>; from flo@rfc822.org on Wed, Feb 20, 2002 at 10:30:12AM +0100
References: <3C6C6ACF.CAD2FFC@mvista.com> <20020215031118.B21011@dea.linux-mips.net> <20020214232030.A3601@mvista.com> <20020215003037.A3670@mvista.com> <002b01c1b607$6afbd5c0$10eca8c0@grendel> <20020219140514.C25739@mvista.com> <00af01c1b9a2$c0d6d5f0$10eca8c0@grendel> <20020219171238.E25739@mvista.com> <15475.24039.877276.257999@gladsmuir.algor.co.uk> <20020220093012.GF11654@paradigm.rfc822.org>
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On Wed, Feb 20, 2002 at 10:30:12AM +0100, Florian Lohoff wrote:

> > It may be heretical... but the lazy FPU context switch was invented
> > for 16MHz CPUs using a write-through cache and non-burst memory, where
> > saving 16 x 64-bit registers took 6us or so (and quite a bit less,
> > later, to read them back).  Call it 8us.
> 
> We are still running on good ol Decstations *snief* Going the way to
> make it SMP only like others archs seem to do it would be good.

While I don't intend to kill support for any of the old machines like
DECstations as long as anybody keeps maintaining support for them
certainly performance tradeoffs in generic code will not be based on
antique systems ...

  Ralf

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