From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265212AbUELUIV (ORCPT ); Wed, 12 May 2004 16:08:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265214AbUELUIV (ORCPT ); Wed, 12 May 2004 16:08:21 -0400 Received: from mx1.elte.hu ([157.181.1.137]:2541 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S265212AbUELUIQ (ORCPT ); Wed, 12 May 2004 16:08:16 -0400 Date: Wed, 12 May 2004 22:03:05 +0200 From: Ingo Molnar To: Davide Libenzi Cc: Jeff Garzik , Greg KH , Andrew Morton , Linux Kernel Mailing List , Netdev Subject: Re: MSEC_TO_JIFFIES is messed up... Message-ID: <20040512200305.GA16078@elte.hu> References: <20040512020700.6f6aa61f.akpm@osdl.org> <20040512181903.GG13421@kroah.com> <40A26FFA.4030701@pobox.com> <20040512193349.GA14936@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.26.8-itk2 (ELTE 1.1) SpamAssassin 2.63 ClamAV 0.65 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Davide Libenzi wrote: > > why is it wrong? > > For HZ == 1000 it's fine, even if it'd better to explicitly make it HZ > dependent and let the compiler to discard them. the compiler cannot discard the multiplication and the division from the following: x * 1000 / 1000 due to overflows. But we know that HZ is 1000 in the arch-dependent param.h, and in sched.c we use the HZ dependent variant: #ifndef JIFFIES_TO_MSEC # define JIFFIES_TO_MSEC(x) ((x) * 1000 / HZ) #endif #ifndef MSEC_TO_JIFFIES # define MSEC_TO_JIFFIES(x) ((x) * HZ / 1000) #endif Ingo