From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932822Ab3E3OZn (ORCPT ); Thu, 30 May 2013 10:25:43 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:26070 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932529Ab3E3OZZ (ORCPT ); Thu, 30 May 2013 10:25:25 -0400 X-IronPort-AV: E=Sophos;i="4.87,770,1363132800"; d="scan'208";a="26908087" From: David Vrabel To: CC: David Vrabel , Konrad Rzeszutek Wilk , John Stultz , Subject: [PATCH 1/2] x86/xen: sync the wallclock when the system time changes Date: Thu, 30 May 2013 15:25:18 +0100 Message-ID: <1369923919-26981-2-git-send-email-david.vrabel@citrix.com> X-Mailer: git-send-email 1.7.2.5 In-Reply-To: <1369923919-26981-1-git-send-email-david.vrabel@citrix.com> References: <1369923919-26981-1-git-send-email-david.vrabel@citrix.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: David Vrabel 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 pvclock_gtod notifier chain to receive a notification when the system time has changed and update the wallclock to match. This chain is called on every timer tick and we want to avoid an extra (expensive) hypercall on every tick. Because dom0 has historically never provided a very accurate wallclock and guests do not expect one, we can do this simply. The wallclock is only updated if the difference between now and the last update is more than 0.5 s. Signed-off-by: David Vrabel --- arch/x86/xen/time.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 46 insertions(+), 0 deletions(-) diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c index a1947ac..60b7d1f 100644 --- a/arch/x86/xen/time.c +++ b/arch/x86/xen/time.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include @@ -212,6 +213,48 @@ static int xen_set_wallclock(const struct timespec *now) return HYPERVISOR_dom0_op(&op); } +static int xen_pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused, + void *priv) +{ + static struct timespec last, next; + struct timespec now; + struct xen_platform_op op; + int ret; + + /* + * Set the Xen wallclock from Linux system time. + * + * dom0 hasn't historically maintained a very accurate + * wallclock so guests don't expect it. We can therefore + * reduce the number of expensive hypercalls by only updating + * the wallclock every 0.5 s. + */ + + now = __current_kernel_time(); + + if (timespec_compare(&now, &last) > 0 + && timespec_compare(&now, &next) < 0) + return 0; + + op.cmd = XENPF_settime; + op.u.settime.secs = now.tv_sec; + op.u.settime.nsecs = now.tv_nsec; + op.u.settime.system_time = xen_clocksource_read(); + + ret = HYPERVISOR_dom0_op(&op); + if (ret) + return 0; + + last = now; + next = timespec_add(now, ns_to_timespec(NSEC_PER_SEC / 2)); + + return 0; +} + +static struct notifier_block xen_pvclock_gtod_notifier = { + .notifier_call = xen_pvclock_gtod_notify, +}; + static struct clocksource xen_clocksource __read_mostly = { .name = "xen", .rating = 400, @@ -473,6 +516,9 @@ static void __init xen_time_init(void) xen_setup_runstate_info(cpu); xen_setup_timer(cpu); xen_setup_cpu_clockevents(); + + if (xen_initial_domain()) + pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier); } void __init xen_init_time_ops(void) -- 1.7.2.5