From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030236AbWGYX0Q (ORCPT ); Tue, 25 Jul 2006 19:26:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030252AbWGYX0Q (ORCPT ); Tue, 25 Jul 2006 19:26:16 -0400 Received: from mail-in-08.arcor-online.net ([151.189.21.48]:47061 "EHLO mail-in-08.arcor-online.net") by vger.kernel.org with ESMTP id S1030236AbWGYX0P (ORCPT ); Tue, 25 Jul 2006 19:26:15 -0400 In-Reply-To: <20060725194733.GJ4608@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> Mime-Version: 1.0 (Apple Message framework v750) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: Cc: "H. Peter Anvin" , linux-kernel@vger.kernel.org, a.zummo@towertech.it, jg@freedesktop.org Content-Transfer-Encoding: 7bit From: Segher Boessenkool Subject: Re: [PATCH] RTC: Add mmap method to rtc character driver Date: Wed, 26 Jul 2006 01:26:07 +0200 To: Neil Horman X-Mailer: Apple Mail (2.750) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org >> But userland cannot know if there is a more efficient option to >> use than this /dev/rtc way, without using VDSO/vsyscall. >> > Sure, but detecting if /dev/rtc via mmap is faster than > gettimeofday is an > orthogonal issue to having the choice in the first place. No it's not. Userland can not detect things it doesn't know about, and then when there is a great choice, it won't see it, and use the 6000kW solution (or any other really bad thing) instead. Using the old old legacy stuff when there's nothing better around is a fine idea; please just implement an x86 VDSO that does just that. x86 is what you care about IIUC. Don't saddle up non-x86 systems that just happen to have a legacy RTC around, and perhaps x86 systems that don't sanely expose their better interfaces, with this quite suboptimal solution for years to come. Segher