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Date: Tue, 12 May 2009 13:40:57 +0100
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Ocamlopt x86-32 and SSE2
Message-ID: <20090512124057.GA598@annexia.org>
References: <20090511043120.976EBBC67@yquem.inria.fr> <B1CD096B-910F-41B7-BBE8-5F2EA0DB49AF@cea.fr> <4A09434D.3020102@inria.fr>
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From: Richard Jones <rich@annexia.org>
X-Spam: no; 0.00; ocamlopt:01 0200,:01 low-power:01 decoding:01 ergo:01 vmware:01 cpuinfo:01 flags:01 vmware:01 packagers:01 ocaml:01 2009:98 wrote:01 caml-list:01 emulate:01 

On Tue, May 12, 2009 at 11:37:17AM +0200, Xavier Leroy wrote:
> Richard Jones:
> >AMD Geode then ...
> 
> Apparently, recent versions of the Geode support SSE2 as well.
> Low-power people love vector instruction sets, because it lets them do
> common tasks like audio and video decoding more efficiently, ergo with
> less energy.

I was mostly joking about this - don't worry :-)

> Well, either
> that, or rely on the kernel to trap unimplemented SSE2 instructions
> and emulate them in software.  This is theoretically possible but I'm
> pretty sure neither Linux nor Windows implement it.

<aside>
Even VMWare aren't doing this.  However, it's now relatively common to
have the CPU lie about the true capabilities of its instruction set
(by faking the return from CPUID, which in Linux means that
/proc/cpuinfo flags doesn't give the true picture).  This is done so
that guests can be migrated across machines in a cluser which have
different capabilities.  VMWare called this 'EVC clustering'.
</aside>

> To finish: I'm still very interested in hearing from packagers.  Does
> Debian, for example, already have some packages that are SSE2-only?
> Are these packages specially tagged so that the installer will refuse
> to install them on pre-SSE2 hardware?  What's the party line?

>>From the Fedora p.o.v., there's no problem.  We'll just deprecate
OCaml on ancient pre-SSE2 hardware (for new distributions - they can
keep using RHEL 5 on older hardware).

Rich.

-- 
Richard Jones
Red Hat