From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757367Ab2ECPuw (ORCPT ); Thu, 3 May 2012 11:50:52 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:34976 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756170Ab2ECPuv (ORCPT ); Thu, 3 May 2012 11:50:51 -0400 Message-ID: <4FA2A8DC.10905@linaro.org> Date: Thu, 03 May 2012 08:48:44 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1 MIME-Version: 1.0 To: Richard Cochran CC: linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [PATCH RFC V1 0/5] Rationalize time keeping References: <4F9B228F.90903@linaro.org> <20120428080443.GA2241@netboy.at.omicron.at> <4F9EFC70.50405@linaro.org> <20120503070139.GA2235@netboy.at.omicron.at> In-Reply-To: <20120503070139.GA2235@netboy.at.omicron.at> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12050315-3270-0000-0000-00000609DF6B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/2012 12:02 AM, Richard Cochran wrote: > On Mon, Apr 30, 2012 at 01:56:16PM -0700, John Stultz wrote: >> No. So, on architectures that support vsyscalls/vdso (x86_64, >> powerpc, ia64, and maybe a few others) getnstimeofday() is really >> only an internal interface for in-kernel access. Userland uses the >> vsyscall/vdso interface to be able to read the time completely from >> userland context (with no syscall overhead). Since this is done in >> different ways for each architecture, you need to export the proper >> information out via update_vsyscall() and also update the >> arch-specific vsyscall gettimeofday paths (which is non-trivial, as >> some arches are implemented in asm, etc - my sympathies here, its a >> pain). > Okay, so now I understand the vDSO page thingy. Help me please to > understand exactly which architectures would need changes for my > proposal. > > The only archs exporting time variables/functions through vDSO are > those which define CONFIG_GENERIC_TIME_VSYSCALL=y, namely: > > - ia64 > - powerpc 64 and 32 bit > - s390 64 and 32 bit > - x86 64 bit only ** > > ** But 32 guest running in a 64 host also has time in the vDSO?!? Yes, but at least on x86 its just one implementation that needs to be modified. > > Did I get that right? That looks right to me. thanks -john