From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <12f7bf2af3e9fd212dd65a508a614428@plan9.bell-labs.com>
Date: Sat, 29 Oct 2005 16:01:36 -0400
From: jmk@plan9.bell-labs.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] 386
In-Reply-To: <20051029190745.GE38291@mero.morphisms.net>
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We're testing a rewrite of the x86 VM system and invlpg
is much less expensive than the alternative of flushing
the entire TLB for temporary mappings. I've been using
invlpg in the old VM system for a while but the code has
to have tests for processor type.

I'd actually like to go further and only support processors
that have the CPUID instruction (that includes the plain
Pentium otherwise my home machine would need to be replaced).

We could provide instructions for what to do if someone
desperately wanted to run the system on deprecated hardware,
it's not hard but I feel it's not worth keeping the support
in the main tree. Also, I can't find the old AT&T Safari
and Gateway Nomad laptops I kept around for testing 386
and 486 compatibility so we've no way to test on those
any more.

--jim

On Sat Oct 29 15:08:57 EDT 2005, jkw@eecs.harvard.edu wrote:
> On Sat, Oct 29, 2005 at 11:08:18AM -0400, Russ Cox wrote:
> > Is anyone out there using Plan 9 on 386 machines?
> > I'm just wondering whether it's going to affect anyone
> > if the default kernels assume they can use some of
> > the 486 instructions (specifically INVLPG).
> 
> I am not and for some things I'm working on, I've given
> up and assumed a PentiumPro.  That said, it would be
> nice to retain support for older machines.
> 
> It has been a while since I've looked at Plan 9's VM
> system.  How hard would it be to select an implementation
> at run time?  It isn't too hard to probe for these sorts
> of things at boot.  I suppose one could also make it a
> compile-time option, but I'd be inclined to avoid that
> since it could lead to a real mess if people decided that
> they wanted to use other features down the road.
> 
> Why the sudden interest in invlpg?