From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751598AbWGYVUa (ORCPT ); Tue, 25 Jul 2006 17:20:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964859AbWGYVUa (ORCPT ); Tue, 25 Jul 2006 17:20:30 -0400 Received: from terminus.zytor.com ([192.83.249.54]:43191 "EHLO terminus.zytor.com") by vger.kernel.org with ESMTP id S1751598AbWGYVU3 (ORCPT ); Tue, 25 Jul 2006 17:20:29 -0400 Message-ID: <44C68AA8.6080702@zytor.com> Date: Tue, 25 Jul 2006 14:18:32 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 1.5.0.4 (X11/20060614) MIME-Version: 1.0 To: jg@laptop.org CC: Neil Horman , Dave Airlie , Segher Boessenkool , linux-kernel@vger.kernel.org, a.zummo@towertech.it, jg@freedesktop.org Subject: Re: [PATCH] RTC: Add mmap method to rtc character driver 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> <1153861094.1230.20.camel@localhost.localdomain> <44C6875F.4090300@zytor.com> <1153862087.1230.38.camel@localhost.localdomain> In-Reply-To: <1153862087.1230.38.camel@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jim Gettys wrote: > On Tue, 2006-07-25 at 14:04 -0700, H. Peter Anvin wrote: > >> That's why I'm suggesting adding a cheap, possibly low-res, gettimeofday >> virtual system call in case there is no way for the kernel to provide >> userspace with a cheap full-resolution gettimeofday. Obviously, if a >> high-quality gettimeofday is available, then they can be linked together >> by the kernel. > > Low res is fine: X Timestamps are 1 millisecond values, and wrap after a > few hundred days. What we do care about is monotonically increasing > values (until it wraps). On machines of the past, this was very > convenient; we'd just store a 32 bit value for clients to read, and not > bother with locking. I guess these days, you'd at least have to protect > the store with a memory barrier, maybe.... > > It was amusing years ago to find toolkit bugs after applications had > been up for that long (32 bits of milliseconds)... Yes, there are > applications and machines that stay up that long, really there are.... > Do you need 1 ms resolution, or is 10 ms good enough? -hpa