From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934720Ab3FSQwM (ORCPT ); Wed, 19 Jun 2013 12:52:12 -0400 Received: from mail-pb0-f48.google.com ([209.85.160.48]:50105 "EHLO mail-pb0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756805Ab3FSQwJ (ORCPT ); Wed, 19 Jun 2013 12:52:09 -0400 Message-ID: <51C1E1B6.8090203@linaro.org> Date: Wed, 19 Jun 2013 09:52:06 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: David Vrabel CC: xen-devel@lists.xen.org, Konrad Rzeszutek Wilk , linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [PATCH 2/4] time: add a notifier chain for when the system time is stepped References: <1371655523-15609-1-git-send-email-david.vrabel@citrix.com> <1371655523-15609-3-git-send-email-david.vrabel@citrix.com> In-Reply-To: <1371655523-15609-3-git-send-email-david.vrabel@citrix.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/19/2013 08:25 AM, 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. > > Add a clock_was_set atomic notifier chain > (clock_was_set_notifier_list) and call this in place of > clock_was_set(). If the timekeeping locks are held, the calls are > deferred to a new tasklet. > > The hrtimer code adds a notifier block to this chain and uses it to > call (the now internal) clock_was_set(). Since the timekeeping code > does not call the chain from the timer irq clock_was_set_delayed() and > associated code can be removed. So on my initial quick review, this *looks* pretty reasonable. I get a little worried about interface abuse (ie: random drivers trying to hook into clock_was_set_notifier_list), but we can move that into timekeeper_internal.h or something similar to limit that. The other issue here is we've been burned pretty badly in the past with changes to clock_was_set(), as its key to keeping timers in line with timekeeping. So this will need a fair amount of testing and run time before this gets merged, so 3.12 is what we'd be targeting at the earliest (its getting a bit late for taking changes for 3.11 anyway). If you want to try to push patch 1/4 in for 3.11 via the Xen tree, I'll see about queuing the other three for hopefully 3.12. thanks -john