Commit 47433b8c authored by David Vrabel's avatar David Vrabel Committed by Thomas Gleixner
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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: default avatarDavid 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: default avatarThomas Gleixner <tglx@linutronix.de>
parent 5584880e

arch/x86/xen/time.c

+26 −19
Original line number Original line Diff line number Diff line
@@ -199,37 +199,42 @@ static void xen_get_wallclock(struct timespec *now) 




static int xen_set_wallclock(const 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;

	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);

}

}





static int xen_pvclock_gtod_notify(struct notifier_block *nb, unsigned long was_set,

static int xen_pvclock_gtod_notify(struct notifier_block *nb,

				   void *priv)

				   unsigned long was_set, void *priv)

{

{

	struct timespec now;

	/* Protected by the calling core code serialization */

	struct xen_platform_op op;

	static struct timespec next_sync;





	if (!was_set)

	struct xen_platform_op op;

		return NOTIFY_OK;

	struct timespec now;





	now = __current_kernel_time();

	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.cmd = XENPF_settime;

	op.u.settime.secs = now.tv_sec;

	op.u.settime.secs = now.tv_sec;

	op.u.settime.nsecs = now.tv_nsec;

	op.u.settime.nsecs = now.tv_nsec;

	op.u.settime.system_time = xen_clocksource_read();

	op.u.settime.system_time = xen_clocksource_read();





	(void)HYPERVISOR_dom0_op(&op);

	(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;

	return NOTIFY_OK;

}

}
@@ -513,6 +518,8 @@ void __init xen_init_time_ops(void) 




	x86_platform.calibrate_tsc = xen_tsc_khz;

	x86_platform.calibrate_tsc = xen_tsc_khz;

	x86_platform.get_wallclock = xen_get_wallclock;

	x86_platform.get_wallclock = xen_get_wallclock;

	/* Dom0 uses the native method to set the hardware RTC. */

	if (!xen_initial_domain())

		x86_platform.set_wallclock = xen_set_wallclock;

		x86_platform.set_wallclock = xen_set_wallclock;

}

}

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