Subject: Re: Prentium MMX for NetBSD-current
To: Jason Thorpe <>
From: Chris G. Demetriou <>
List: current-users
Date: 01/17/1997 16:15:12
> On Fri, 17 Jan 1997 13:47:49 -0500 
>  "Chris G. Demetriou" <> wrote:
>  > So, every time the FreeBSD VM system comes up, somebody from NetBSD
>  > says that "it has portability problems," and invariably somebody from
>  > FreeBSD says "no it doesn't."
> I am going on comments made to me by Matt Green, who did a fair
> amount of work to attempt a port of the FreeBSD VM code to NetBSD,
> and by others who have mentioned their intent to write
> a veneer layer to make MMUs on other architectures emulate
> the i386 MMU.

So, why don't they speak up and voice their specific concerns?

Whining about code and justifying it with hearsay is... well, not too
cool, in my opinion.

> The latter is what concerns me the most; in the
> Mach portability model, the pmap module is supposed to hide
> machine-dependencies.  If this is the case, why bother emulating
> another MMU?

Uh, how about "because pmap modules are a bitch to write"?

If you're using that as a metric for concern, then you should be
concerned about NetBSD, as well.  For instance, the NetBSD/alpha pmap
code effectively treats the alpha MMU like an '030 MMU (with a few
minor tweaks to deal with reference/modify emulation), because that
was (much!) easier than writing a "proper" pmap.  (Eventually, i'll
get around to doing the right thing, but...)