From owner-svn-src-all@FreeBSD.ORG  Thu Jun 17 12:44:30 2010
Return-Path: <owner-svn-src-all@FreeBSD.ORG>
Delivered-To: svn-src-all@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 09C02106566C;
	Thu, 17 Jun 2010 12:44:30 +0000 (UTC)
	(envelope-from brde@optusnet.com.au)
Received: from mail09.syd.optusnet.com.au (mail09.syd.optusnet.com.au
	[211.29.132.190])
	by mx1.freebsd.org (Postfix) with ESMTP id 7016F8FC0C;
	Thu, 17 Jun 2010 12:44:29 +0000 (UTC)
Received: from c122-106-175-69.carlnfd1.nsw.optusnet.com.au
	(c122-106-175-69.carlnfd1.nsw.optusnet.com.au [122.106.175.69])
	by mail09.syd.optusnet.com.au (8.13.1/8.13.1) with ESMTP id
	o5HCiPwK009548
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
	Thu, 17 Jun 2010 22:44:26 +1000
Date: Thu, 17 Jun 2010 22:44:25 +1000 (EST)
From: Bruce Evans <brde@optusnet.com.au>
X-X-Sender: bde@delplex.bde.org
To: Kostik Belousov <kostikbel@gmail.com>
In-Reply-To: <20100617071300.GX13238@deviant.kiev.zoral.com.ua>
Message-ID: <20100617223406.B40711@delplex.bde.org>
References: <201006130239.o5D2du3m086332@svn.freebsd.org>
	<20100613101025.GD1320@garage.freebsd.pl> <4C158B71.205@freebsd.org>
	<20100614085205.GD13238@deviant.kiev.zoral.com.ua>
	<4C1605A7.2000202@freebsd.org>
	<20100614104349.GF13238@deviant.kiev.zoral.com.ua>
	<4C198A90.3060905@freebsd.org>
	<20100617071300.GX13238@deviant.kiev.zoral.com.ua>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Cc: Matthew Fleming <mdf@FreeBSD.org>, src-committers@FreeBSD.org,
	Pawel Jakub Dawidek <pjd@FreeBSD.org>,
	John Baldwin <jhb@FreeBSD.org>, svn-src-all@FreeBSD.org,
	brde@optusnet.com.au, svn-src-head@FreeBSD.org,
	Lawrence Stewart <lstewart@FreeBSD.org>
Subject: Re: svn commit: r209119 - head/sys/sys
X-BeenThere: svn-src-all@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: "SVN commit messages for the entire src tree \(except for &quot;
	user&quot; and &quot; projects&quot; \)" <svn-src-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
	<mailto:svn-src-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all>
List-Post: <mailto:svn-src-all@freebsd.org>
List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
	<mailto:svn-src-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 17 Jun 2010 12:44:30 -0000

On Thu, 17 Jun 2010, Kostik Belousov wrote:

> On Thu, Jun 17, 2010 at 12:38:08PM +1000, Lawrence Stewart wrote:
>> I've tested the above and it works. I also prefer the idea of having
>> DPCPU_SUM return the sum so that you can do "var = DPCPU_SUM(...)". My
>> only concern with this method is that the caller no longer has the
>> choice to make the sum variable a larger type to avoid overflow. It
>> would be nice to be able to have the DPCPU vars be uint32_t but be able
>> to sum them into a uint64_t accumulator for example. Perhaps this isn't
>> really an issue though... I'm not sure.
> You are worried about overflow in the sum of 32 or 64 variables, but if
> this is the case, then each member of the sum can overflow as well, IMO.
> Either ignore the issue, or use a uintmax_t.

Or use int variables so that the overflow trap can work, and fix the
overflow trap to work (gcc -ftapv, but this is unusable in the kernel),
and get a nice panic on all overflows, not just here :-).

Bruce