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Re: FPU emulator unsafe for SMP?

To: Ralf Baechle <ralf@oss.sgi.com>
Subject: Re: FPU emulator unsafe for SMP?
From: Jun Sun <jsun@mvista.com>
Date: Thu, 14 Feb 2002 23:20:30 -0800
Cc: linux-mips@oss.sgi.com
In-reply-to: <20020215031118.B21011@dea.linux-mips.net>; from ralf@oss.sgi.com on Fri, Feb 15, 2002 at 03:11:18AM +0100
References: <3C6C6ACF.CAD2FFC@mvista.com> <20020215031118.B21011@dea.linux-mips.net>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Fri, Feb 15, 2002 at 03:11:18AM +0100, Ralf Baechle wrote:
> On Thu, Feb 14, 2002 at 05:56:31PM -0800, Jun Sun wrote:
> 
> > I have been chasing a FPU register corruption problem on a SMP box.  The
> > curruption seems to be caused by FPU emulator code.  Is that code SMP safe? 
> > If not, what are the volunerable spots?
> > 
> > Just thought I'd check before I dive into it ....
> 
> In theory the fp emulation code should be MP safe as the full emulation
> is only accessing it's context in the fp register set of struct
> task_struct.  The 32-bit kernel's fp register switching is entirely broken
> (read: close to non-existant).  Lots of brownie points for somebody to
> backport that from the 64-bit kernel to the 32-bit kernel and forward
> port all the FPU emu bits to the 64-bit kernel ...
> 

Brownie sounds good. :-)  So what is the "fp register switching" you are 
referring to?  There is set of code related to lazy fpu context switch,
which seems to be working fine now.

Jun

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