From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754128Ab2IARDN (ORCPT ); Sat, 1 Sep 2012 13:03:13 -0400 Received: from zoneX.GCU-Squad.org ([194.213.125.0]:11442 "EHLO services.gcu-squad.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751761Ab2IARDL (ORCPT ); Sat, 1 Sep 2012 13:03:11 -0400 Date: Sat, 1 Sep 2012 19:02:54 +0200 From: Jean Delvare To: Andrew Morton Cc: Guenter Roeck , linux-kernel@vger.kernel.org, Pekka Enberg , Ingo Molnar , "H. Peter Anvin" , lm-sensors@lm-sensors.org Subject: Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends Message-ID: <20120901190254.108e3f6b@endymion.delvare> In-Reply-To: <20120831123812.62729e1c.akpm@linux-foundation.org> References: <1346425339-17138-1-git-send-email-linux@roeck-us.net> <20120831123812.62729e1c.akpm@linux-foundation.org> X-Mailer: Claws Mail 3.7.10 (GTK+ 2.24.7; x86_64-suse-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andrew, Guenter, On Fri, 31 Aug 2012 12:38:12 -0700, Andrew Morton wrote: > On Fri, 31 Aug 2012 08:02:19 -0700 > Guenter Roeck wrote: > > > DIV_ROUND_CLOSEST returns a bad result for negative dividends: > > DIV_ROUND_CLOSEST(-2, 2) = 0 > > > > Most of the time this does not matter. However, in the hardware monitoring > > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be > > negative (such as temperatures). > > > > ... > > > > + > > +/* > > + * Divide positive or negative dividend by positive divisor and round > > + * to closest integer. Result is undefined for negative divisors. > > + */ > > #define DIV_ROUND_CLOSEST(x, divisor)( \ > > { \ > > - typeof(divisor) __divisor = divisor; \ > > - (((x) + ((__divisor) / 2)) / (__divisor)); \ > > + typeof(x) __x = x; \ > > + typeof(divisor) __d = divisor; \ > > + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \ > > + (((__x) + ((__d) / 2)) / (__d)) : \ > > + (((__x) - ((__d) / 2)) / (__d)); \ > > } \ > > Looks good to me. My testing looks good too. Acked-by: Jean Delvare > The patch causes no change in text size for > kernel/sched/fair.o and drivers/cpuidle/governors/menu.o, so it seems > that the cc trickery is working. Indeed. I looked for test size increase, and for my config, besides hwmon, I only spotted the following ones: drivers/media/rc/mceusb.o drivers/gpu/drm/i915/intel_pm.o drivers/tty/serial/pch_uart.o These don't look like hot paths, so I'd say we don't care. Plus the intel_pm one can probably be solved by using an unsigned int, I don't see why/how ia_freq could be negative (negative frequency anyone?) And for mceusb it can be solved easily by changing "1" to "1U". For hwmon drivers, we typically only use DIV_ROUND_CLOSEST when the user changes a setting, this isn't a frequent event. Plus, this is exactly the case we are fixing here, as temperature limits, and to a lesser extent voltage limits, can be negative. > I'll add it to my tree for testing - please merge this via your tree. -- Jean Delvare