From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762943AbZJOTUA (ORCPT ); Thu, 15 Oct 2009 15:20:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761693AbZJOTT7 (ORCPT ); Thu, 15 Oct 2009 15:19:59 -0400 Received: from claw.goop.org ([74.207.240.146]:44181 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761606AbZJOTT6 (ORCPT ); Thu, 15 Oct 2009 15:19:58 -0400 Message-ID: <4AD775BA.30704@goop.org> Date: Thu, 15 Oct 2009 12:19:22 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20090922 Fedora/3.0-2.7.b4.fc11 Lightning/1.0pre Thunderbird/3.0b4 MIME-Version: 1.0 To: Dan Magenheimer CC: Xen-devel , kurt.hackel@oracle.com, arch/x86 maintainers , Linux Kernel Mailing List , Glauber de Oliveira Costa , Avi Kivity , chris.mason@oracle.com Subject: Re: [Xen-devel] [PATCH 05/12] xen/pvclock: add monotonicity check References: In-Reply-To: X-Enigmail-Version: 0.97a Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/15/09 06:27, Dan Magenheimer wrote: > I understand but you are now essentially emulating a > reliable platform timer with a potentially unreliable > (but still high resolution) per-CPU timer AND probably > delivering that result to userland. > > Read_tsc should only be used if either CONSTANT_TSC > or TSC_RELIABLE is true, so read_tsc is guaranteed > to be monotonically-strictly-increasing by hardware > (and enforced for CONSTANT_TSC by check_tsc_warp > at boot). > read_tsc clearly isn't expected to produce absolutely globally monotonic results; if it were then the check wouldn't be necessary. J From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [PATCH 05/12] xen/pvclock: add monotonicity check Date: Thu, 15 Oct 2009 12:19:22 -0700 Message-ID: <4AD775BA.30704@goop.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Dan Magenheimer Cc: Xen-devel , kurt.hackel@oracle.com, arch/x86 maintainers , Linux Kernel Mailing List , Glauber de Oliveira Costa , Avi Kivity , chris.mason@oracle.com List-Id: xen-devel@lists.xenproject.org On 10/15/09 06:27, Dan Magenheimer wrote: > I understand but you are now essentially emulating a > reliable platform timer with a potentially unreliable > (but still high resolution) per-CPU timer AND probably > delivering that result to userland. > > Read_tsc should only be used if either CONSTANT_TSC > or TSC_RELIABLE is true, so read_tsc is guaranteed > to be monotonically-strictly-increasing by hardware > (and enforced for CONSTANT_TSC by check_tsc_warp > at boot). > read_tsc clearly isn't expected to produce absolutely globally monotonic results; if it were then the check wouldn't be necessary. J