From owner-freebsd-current  Wed Nov 29 15:20:34 2000
Delivered-To: freebsd-current@freebsd.org
Received: from mail.interware.hu (mail.interware.hu [195.70.32.130])
	by hub.freebsd.org (Postfix) with ESMTP id 3AACA37B404
	for <current@freebsd.org>; Wed, 29 Nov 2000 15:20:31 -0800 (PST)
Received: from monrovia-58.budapest.interware.hu ([195.70.53.250] helo=elischer.org)
	by mail.interware.hu with esmtp (Exim 3.16 #1 (Debian))
	id 141GWX-0004eH-00; Thu, 30 Nov 2000 00:20:26 +0100
Message-ID: <3A2525DD.3D1E8D5A@elischer.org>
Date: Wed, 29 Nov 2000 07:50:53 -0800
From: Julian Elischer <julian@elischer.org>
X-Mailer: Mozilla 4.7 [en] (X11; U; FreeBSD 5.0-CURRENT i386)
X-Accept-Language: en, hu
MIME-Version: 1.0
To: Bruce Evans <bde@zeta.org.au>
Cc: current@FreeBSD.ORG
Subject: Re: slight improvement in locore.s?
References: <Pine.BSF.4.21.0011291824440.2767-100000@besplex.bde.org>
Content-Type: text/plain; charset=iso-8859-15
Content-Transfer-Encoding: 7bit
Sender: owner-freebsd-current@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

Bruce Evans wrote:
> 
> On Thu, 23 Nov 2000, Julian Elischer wrote:
> 
> > locore.s includes:
> > #define ALLOCPAGES(foo) \
> >         movl    R(physfree), %esi ; \
> >         movl    $((foo)*PAGE_SIZE), %eax ; \
> >         addl    %esi, %eax ; \
> >         movl    %eax, R(physfree) ; \
> >         movl    %esi, %edi ; \
> >         movl    $((foo)*PAGE_SIZE),%ecx ; \
> >         xorl    %eax,%eax ; \
> >         cld ; \
> >         rep ; \
> >         stosb
> >
> >
> > might it be a very slight optimisation to change this to:
> > #define ALLOCPAGES(foo) \
> >         movl    R(physfree), %esi ; \
> >         movl    $((foo)*PAGE_SIZE), %eax ; \
> >         movl    %eax, %ecx ; \
> >         addl    %esi, %eax ; \
> >         movl    %eax, R(physfree) ; \
> >         movl    %esi, %edi ; \
> >         xorl    %eax,%eax ; \
> >         cld ; \
> >         rep ; \
> >         stosb
> 
> This can be improved more (3 instructions) by not loading physfree into
> the wrong register, and depending on stosb to increment the register,


so your assembly code would look like? (just curious).

> but it should be written in C anyway.  A relocation macro like R()
> should work just as well in C as in asm.  In C, the above is:
> 
>         bzero(R(physfree), (foo) * PAGE_SIZE);
>         R(physfree) += (foo) * PAGE_SIZE);
>         return (R(physfree));   /* In unusual as well as wrong reg %esi. */
> 
> Bruce

-- 
      __--_|\  Julian Elischer
     /       \ julian@elischer.org
    (   OZ    ) World tour 2000
---> X_.---._/  presently in:  Budapest
            v




To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message