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