From owner-svn-src-head@FreeBSD.ORG  Mon Apr 20 13:39:44 2009
Return-Path: <owner-svn-src-head@FreeBSD.ORG>
Delivered-To: svn-src-head@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 2108A1065687;
	Mon, 20 Apr 2009 13:39:44 +0000 (UTC)
	(envelope-from rwatson@FreeBSD.org)
Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42])
	by mx1.freebsd.org (Postfix) with ESMTP id E9A7D8FC1F;
	Mon, 20 Apr 2009 13:39:43 +0000 (UTC)
	(envelope-from rwatson@FreeBSD.org)
Received: from fledge.watson.org (fledge.watson.org [65.122.17.41])
	by cyrus.watson.org (Postfix) with ESMTPS id 9E01E46B23;
	Mon, 20 Apr 2009 09:39:43 -0400 (EDT)
Date: Mon, 20 Apr 2009 14:39:43 +0100 (BST)
From: Robert Watson <rwatson@FreeBSD.org>
X-X-Sender: robert@fledge.watson.org
To: Bruce Evans <brde@optusnet.com.au>
In-Reply-To: <20090420174802.F58065@delplex.bde.org>
Message-ID: <alpine.BSF.2.00.0904201438380.82842@fledge.watson.org>
References: <200904192019.n3JKJDa6019179@svn.freebsd.org>
	<20090420174802.F58065@delplex.bde.org>
User-Agent: Alpine 2.00 (BSF 1167 2008-08-23)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org,
	src-committers@FreeBSD.org
Subject: Re: svn commit: r191276 - in head/sys: amd64/include arm/include
 i386/include ia64/include mips/include powerpc/include sparc64/include
 sun4v/include
X-BeenThere: svn-src-head@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: SVN commit messages for the src tree for head/-current
	<svn-src-head.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-head>,
	<mailto:svn-src-head-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-head>
List-Post: <mailto:svn-src-head@freebsd.org>
List-Help: <mailto:svn-src-head-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-head>,
	<mailto:svn-src-head-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 20 Apr 2009 13:39:48 -0000


On Mon, 20 Apr 2009, Bruce Evans wrote:

>> +#ifndef CACHE_LINE_SHIFT
>> +#define	CACHE_LINE_SHIFT	6
>> +#endif
>> +#define	CACHE_LINE_SIZE		(1 << CACHE_LINE_SHIFT)
>
> This still has the bogus ifdef.  Overriding the definition is difficult to 
> do consistently even in a kernel with no modules, since CACHE_LINE_SIZE is 
> not a kernel option.  Overriding the definition makes negative sense since 
> the value is a maximum-maximum (possibly larger than strictly needed) so 
> that it can be constant.

OK, I've made this change.  My hope is that most applications don't resort to 
including sys/param.h and using CACHE_LINE_SIZE -- most will be able to query 
it at run-time using interfaces we don't yet have (such as sysconf(3) and some 
appropriate constant).  I also hope that most kernel consumers will be able to 
use a run-time tuned version (which we also don't yet have).

Robert N M Watson
Computer Laboratory
University of Cambridge