From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751592AbWGYU6U (ORCPT ); Tue, 25 Jul 2006 16:58:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751593AbWGYU6T (ORCPT ); Tue, 25 Jul 2006 16:58:19 -0400 Received: from rwcrmhc12.comcast.net ([204.127.192.82]:62598 "EHLO rwcrmhc12.comcast.net") by vger.kernel.org with ESMTP id S1751591AbWGYU6T (ORCPT ); Tue, 25 Jul 2006 16:58:19 -0400 Subject: Re: [PATCH] RTC: Add mmap method to rtc character driver From: Jim Gettys Reply-To: jg@laptop.org To: Neil Horman Cc: "H. Peter Anvin" , Dave Airlie , Segher Boessenkool , linux-kernel@vger.kernel.org, a.zummo@towertech.it, jg@freedesktop.org In-Reply-To: <20060725204736.GK4608@hmsreliant.homelinux.net> References: <20060725174100.GA4608@hmsreliant.homelinux.net> <03BCDC7F-13D9-42FC-86FC-30C76FD3B3B8@kernel.crashing.org> <20060725182833.GE4608@hmsreliant.homelinux.net> <44C66C91.8090700@zytor.com> <20060725192138.GI4608@hmsreliant.homelinux.net> <20060725194733.GJ4608@hmsreliant.homelinux.net> <21d7e9970607251304n5681bf44gc751c21fd79be99d@mail.gmail.com> <44C67E1A.7050105@zytor.com> <20060725204736.GK4608@hmsreliant.homelinux.net> Content-Type: text/plain Organization: OLPC Date: Tue, 25 Jul 2006 16:58:14 -0400 Message-Id: <1153861094.1230.20.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2006-07-25 at 16:47 -0400, Neil Horman wrote: > > > > The i386 vdso right now has only two entry points, as far as I can > tell: > > system call and signal return. > > > > There is no reason it couldn't have more than that. A > low-resolution > > and a high-resolution gettimeofday might be a good idea. > > > > -hpa > > Agreed. How about we take the /dev/rtc patch now (since its an added > feature > that doesn't hurt anything if its not used, as far as tickless kernels > go), and > I'll start working on doing gettimeofday in vdso for arches other than > x86_64. > That will give the X guys what they wanted until such time until all > the other > arches have a gettimeofday alternative that doesn't require kernel > traps. > Some of us want/need both tickless and smart scheduling in the X server. To give a bit of data: on my machine, a 1x1 rectangle can go almost 2 million rectangles/second; a 500x500 rectangle is only 2800/second. You can see the tremendous variation (and this is on accelerated hardware; the variation can in fact be much larger than this, if the operation has to be done in software fall-backs). This is why the X server needs to know the time so much, so cheaply; we have to be able to tell how much time a given client has been using, and it can't be computed from anything but the time; otherwise individual clients can "starve" other clients, and interactive feel goes to pot. - Jim -- Jim Gettys One Laptop Per Child