Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758119Ab2JZJzW (ORCPT ); Fri, 26 Oct 2012 05:55:22 -0400 Received: from casper.infradead.org ([85.118.1.10]:40454 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754281Ab2JZJzU convert rfc822-to-8bit (ORCPT ); Fri, 26 Oct 2012 05:55:20 -0400 Message-ID: <1351245264.16863.12.camel@twins> Subject: Re: [PATCH 01/16] math128: Introduce various 128bit primitives From: Peter Zijlstra To: Ingo Molnar 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 Date: Fri, 26 Oct 2012 11:54:24 +0200 In-Reply-To: <20121026094207.GA2179@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> <20121026092421.GB628@gmail.com> <1351244130.16863.7.camel@twins> <20121026094207.GA2179@gmail.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1552 Lines: 39 On Fri, 2012-10-26 at 11:42 +0200, Ingo Molnar wrote: > * Peter Zijlstra wrote: > > > On Fri, 2012-10-26 at 11:24 +0200, Ingo Molnar wrote: > > > > > 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. > > > > I _think_ something like: dl_runtime * dl_deadline < U64_MAX, > > might do that. The question is, is this constraint usable? > > Simplified that boils down to about 4 seconds each, which > > sounds pretty much ok for most people -- but such statements > > usually come back to bite you (640kb anybody...). > > We could constrain the precision, not the maximum value. > > Having a 4 seconds hard limit is one thing, only having 10 nsecs > precision at 40 seconds is another. That gets to be rather ugly I think.. for one it might surprise people, secondly you get to have a bunch of conditionals and shifts in that code path. Personally I'd prefer to do the simple thing, esp. for a new interface. So either do the hard limit or the u128 thing. If we go with the hard limit, we can always address things when people run into it and complain, at such a time we also have a better view of people's uses and expectations methinks. -- 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/