Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755955Ab2JZJYa (ORCPT ); Fri, 26 Oct 2012 05:24:30 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:38404 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752852Ab2JZJY1 (ORCPT ); Fri, 26 Oct 2012 05:24:27 -0400 Date: Fri, 26 Oct 2012 11:24:21 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: Linus Torvalds , Juri Lelli , tglx@linutronix.de, mingo@redhat.com, rostedt@goodmis.org, oleg@redhat.com, fweisbec@gmail.com, darren@dvhart.com, johan.eker@ericsson.com, p.faure@akatech.ch, linux-kernel@vger.kernel.org, claudio@evidence.eu.com, michael@amarulasolutions.com, fchecconi@gmail.com, tommaso.cucinotta@sssup.it, nicola.manica@disi.unitn.it, luca.abeni@unitn.it, dhaval.giani@gmail.com, hgu1972@gmail.com, paulmck@linux.vnet.ibm.com, raistlin@linux.it, insop.song@ericsson.com, liming.wang@windriver.com, jkacur@redhat.com, harald.gustafsson@ericsson.com, vincent.guittot@linaro.org, Andrew Morton Subject: Re: [PATCH 01/16] math128: Introduce various 128bit primitives Message-ID: <20121026092421.GB628@gmail.com> References: <1351115634-8420-1-git-send-email-juri.lelli@gmail.com> <1351115634-8420-2-git-send-email-juri.lelli@gmail.com> <1351172849.12171.10.camel@twins> <1351241389.12171.45.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1351241389.12171.45.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1220 Lines: 33 * Peter Zijlstra wrote: > On Thu, 2012-10-25 at 15:26 -0700, Linus Torvalds wrote: > > it's the *rest* of the "u128" math I really object to. I also wonder > > about the u64xu64 math case for SCHED_DEADLINE, because I assume that > > it doesn't actually end up using the 128-bit result in that form, but > > scales it down again some way? > > No, it does a compare on two u128, so it doesn't loose any > precision. If it were to scale down again and loose precision > I'd agree with you that introducing the u128 stuff is > pointless. > > The point is (as mentioned in the comments below) overflowing > an actual u64 is rare, however since some of this > (specifically the dl_{runtime,deadline} parameters) is user > specified, we have to assume we will overflow. So can we control this by restricting the users and avoiding the overflow? A 2^64 result should be a *huge* amount of space already for just about anything. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/