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Re: 64-bit and N32 kernel interfaces

To: macro@ds2.pg.gda.pl (Maciej W. Rozycki)
Subject: Re: 64-bit and N32 kernel interfaces
From: Hartvig Ekner <hartvige@mips.com>
Date: Thu, 5 Sep 2002 20:07:03 +0200 (CEST)
Cc: dan@debian.org (Daniel Jacobowitz), hartvige@mips.com (Hartvig Ekner), kevink@mips.com (Kevin D. Kissell), tor@spacetec.no (Tor Arntsen), carstenl@mips.com (Carsten Langgaard), ralf@linux-mips.org (Ralf Baechle), linux-mips@linux-mips.org
In-reply-to: <Pine.GSO.3.96.1020905170830.7444E-100000@delta.ds2.pg.gda.pl> from "Maciej W. Rozycki" at Sep 05, 2002 05:10:51
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
Maciej W. Rozycki writes:
> 
> On Thu, 5 Sep 2002, Daniel Jacobowitz wrote:
> 
> > No - the point is that all data types have the same size in N32.  It
> > was created explicitly as a transitional sop for people who didn't want
> > to fix their code, but wanted a performance increase from their 64-bit
> > hardware.
> 
>  Well, what's the performance increase of n32 over o32?  The increased
> number of argument registers?  I doubt it's noticeable in most cases.

The technical benefits of n32 over o32 are:

* More argument registers => less memory traffic, less D-cache use,
        => faster code

* 64-bit datapath of CPU can be utilized with big impact on certain
  applications

* 32 floating point registers instead of 16 (and more efficient
  parameter passing as well)

/Hartvig

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