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authorDavid Vrabel <david.vrabel@citrix.com>2013-06-27 11:35:48 +0100
committerThomas Gleixner <tglx@linutronix.de>2013-06-28 23:15:07 +0200
commit47433b8c9d7480a3eebd99df38e857ce85a37cee (patch)
treed89d45a5fa0abc84602320d6e19579be73eaad2d /arch
parent5584880e44e49c587059801faa2a9f7d22619c48 (diff)
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x86: xen: Sync the CMOS RTC as well as the Xen wallclock
Adjustments to Xen's persistent clock via update_persistent_clock() don't actually persist, as the Xen wallclock is a software only clock and modifications to it do not modify the underlying CMOS RTC. The x86_platform.set_wallclock hook is there to keep the hardware RTC synchronized. On a guest this is pointless. On Dom0 we can use the native implementaion which actually updates the hardware RTC, but we still need to keep the software emulation of RTC for the guests up to date. The subscription to the pvclock_notifier allows us to emulate this easily. The notifier is called at every tick and when the clock was set. Right now we only use that notifier when the clock was set, but due to the fact that it is called periodically from the timekeeping update code, we can utilize it to emulate the NTP driven drift compensation of update_persistant_clock() for the Xen wall (software) clock. Add a 11 minutes periodic update to the pvclock_gtod notifier callback to achieve that. The static variable 'next' which maintains that 11 minutes update cycle is protected by the core code serialization so there is no need to add a Xen specific serialization mechanism. [ tglx: Massaged changelog and added a few comments ] Signed-off-by: David Vrabel <david.vrabel@citrix.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: John Stultz <john.stultz@linaro.org> Cc: <xen-devel@lists.xen.org> Link: http://lkml.kernel.org/r/1372329348-20841-6-git-send-email-david.vrabel@citrix.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/xen/time.c45
1 files changed, 26 insertions, 19 deletions
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 3364850d23e6..7a5671b4fec6 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -199,37 +199,42 @@ static void xen_get_wallclock(struct timespec *now)
static int xen_set_wallclock(const struct timespec *now)
{
- struct xen_platform_op op;
-
- /* do nothing for domU */
- if (!xen_initial_domain())
- return -1;
-
- 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();
-
- return HYPERVISOR_dom0_op(&op);
+ return -1;
}
-static int xen_pvclock_gtod_notify(struct notifier_block *nb, unsigned long was_set,
- void *priv)
+static int xen_pvclock_gtod_notify(struct notifier_block *nb,
+ unsigned long was_set, void *priv)
{
- struct timespec now;
- struct xen_platform_op op;
+ /* Protected by the calling core code serialization */
+ static struct timespec next_sync;
- if (!was_set)
- return NOTIFY_OK;
+ struct xen_platform_op op;
+ struct timespec now;
now = __current_kernel_time();
+ /*
+ * We only take the expensive HV call when the clock was set
+ * or when the 11 minutes RTC synchronization time elapsed.
+ */
+ if (!was_set && timespec_compare(&now, &next_sync) < 0)
+ return NOTIFY_OK;
+
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();
(void)HYPERVISOR_dom0_op(&op);
+
+ /*
+ * Move the next drift compensation time 11 minutes
+ * ahead. That's emulating the sync_cmos_clock() update for
+ * the hardware RTC.
+ */
+ next_sync = now;
+ next_sync.tv_sec += 11 * 60;
+
return NOTIFY_OK;
}
@@ -513,7 +518,9 @@ void __init xen_init_time_ops(void)
x86_platform.calibrate_tsc = xen_tsc_khz;
x86_platform.get_wallclock = xen_get_wallclock;
- x86_platform.set_wallclock = xen_set_wallclock;
+ /* Dom0 uses the native method to set the hardware RTC. */
+ if (!xen_initial_domain())
+ x86_platform.set_wallclock = xen_set_wallclock;
}
#ifdef CONFIG_XEN_PVHVM