From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757932Ab2JZNJb (ORCPT ); Fri, 26 Oct 2012 09:09:31 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:9137 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753494Ab2JZNJ3 (ORCPT ); Fri, 26 Oct 2012 09:09:29 -0400 X-Authority-Analysis: v=2.0 cv=NLdXCjGg c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=rDHpwsyNOsUA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=HXw8KzeH-oIA:10 a=Eow2fQRh3KNJYC_SyjMA:9 a=PUjeQqilurYA:10 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.115.198 Message-ID: <1351256965.8467.61.camel@gandalf.local.home> Subject: Re: [PATCH 01/16] math128: Introduce various 128bit primitives From: Steven Rostedt To: Thomas Gleixner Cc: Peter Zijlstra , Ingo Molnar , Linus Torvalds , Juri Lelli , mingo@redhat.com, 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 09:09:25 -0400 In-Reply-To: <1351255155.8467.55.camel@gandalf.local.home> 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> <1351245264.16863.12.camel@twins> <1351255155.8467.55.camel@gandalf.local.home> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.4.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2012-10-26 at 08:39 -0400, Steven Rostedt wrote: > On Fri, 2012-10-26 at 12:36 +0200, Thomas Gleixner wrote: > > > By all means. nsec precision is a completly academic thought > > exercise. It's really pointless to even think about anything below > > microseconds resolution. > > > > We can still have the user space interface handing in the information > > in nsec resolution, but it's reasonable to scale it down to something > > useful. Just shift the incoming information right by 10, so you're in > > the 1us resolution for all the internal math and all your limitation > > problems are gone. A shift by ten for converting back and forth to > > nsecs is not a real performance issue. > > Just make sure this is well documented in the man pages, and that should > eliminate any "surprises". This is a new interface, we can just make > this part of the ABI. "The units are in nanoseconds, but all > calculations are performed to the nearest microsecond. Take this into > account for error analysis". People should be fine with this. Actually, a shift by 10 is a division by 1024, which is not truly down to a microsecond. Would just a shift by 9 work as well? This would make the resolution closer to a half of microsecond. Otherwise things will probably get screwy if the user passes in 1000 ns, and gets a zero result. -- Steve