From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161382Ab3FUMlt (ORCPT ); Fri, 21 Jun 2013 08:41:49 -0400 Received: from smtp.citrix.com ([66.165.176.89]:64565 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161196Ab3FUMls (ORCPT ); Fri, 21 Jun 2013 08:41:48 -0400 X-IronPort-AV: E=Sophos;i="4.87,913,1363132800"; d="scan'208";a="32641686" Message-ID: <51C44A09.9010402@citrix.com> Date: Fri, 21 Jun 2013 13:41:45 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20120428 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: Thomas Gleixner CC: , Konrad Rzeszutek Wilk , LKML , John Stultz , Ingo Molnar , Peter Zijlstra Subject: Re: [PATCH 2/4] time: add a notifier chain for when the system time is stepped References: <1371755792-25962-1-git-send-email-david.vrabel@citrix.com> <1371755792-25962-3-git-send-email-david.vrabel@citrix.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/06/13 08:57, Thomas Gleixner wrote: > On Thu, 20 Jun 2013, David Vrabel wrote: > >> From: David Vrabel >> >> The high resolution timer code gets notified of step changes to the >> system time with clock_was_set() or clock_was_set_delayed() calls. If >> other parts of the kernel require similar notification there is no >> clear place to hook into. > > You fail to explain why any other part of the kernel requires a > notification. This is needed by patch 3 in this series. "The Xen wallclock is a software only clock within the Xen hypervisor that is used by: a) PV guests as the equivalent of a hardware RTC; and b) the hypervisor as the clock source for the emulated RTC provided to HVM guests. Currently the Xen wallclock is only updated every 11 minutes if NTP is synchronized to its clock source. If a guest is started before NTP is synchronized it may see an incorrect wallclock time. Use the clock_was_set notifier chain to receive a notification when the system time is stepped and update the wallclock to match the current system time." > We went great length to confine timekeeping inside the core code and > now you add random notifiers along with totally ugly tasklet > constructs. I'm not sure I understand your objection to the use of a tasklet. Using the hrtimer softirq for something that is no longer hrtimer-specific did not seem like the correct thing to do. David