Mailing List Archive: [PATCH 1/3] xen: sync the CMOS RTC as well as the Xen wallclock

[PATCH 1/3] xen: sync the CMOS RTC as well as the Xen wallclock

Oct 12, 2012, 5:57 AM

Post #1 of 3 (144 views)

From: David Vrabel <david.vrabel@citrix.com>

If NTP is used in dom0 and it is synchronized to its clock source,
then the kernel will periodically synchronize the Xen wallclock with
the system time. Updates to the Xen wallclock do not persist across
reboots, so also synchronize the CMOS RTC (as on bare metal).

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
arch/x86/xen/time.c | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 0296a95..5e7f536 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -14,6 +14,7 @@
#include <linux/kernel_stat.h>
#include <linux/math64.h>
#include <linux/gfp.h>
+#include <linux/mc146818rtc.h>

#include <asm/pvclock.h>
#include <asm/xen/hypervisor.h>
@@ -208,6 +209,10 @@ static int xen_set_wallclock(unsigned long now)
if (!xen_initial_domain())
return -1;

+ /* Set the hardware RTC. */
+ mach_set_rtc_mmss(now);
+
+ /* Set the Xen wallclock. */
op.cmd = XENPF_settime;
op.u.settime.secs = now;
op.u.settime.nsecs = 0;
--
1.7.2.5

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Re: [PATCH 1/3] xen: sync the CMOS RTC as well as the Xen wallclock [ In reply to ]

konrad.wilk at oracle

Oct 12, 2012, 7:57 AM

Post #2 of 3 (143 views)

Permalink

On Fri, Oct 12, 2012 at 01:57:12PM +0100, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
>
> If NTP is used in dom0 and it is synchronized to its clock source,
> then the kernel will periodically synchronize the Xen wallclock with
> the system time. Updates to the Xen wallclock do not persist across
> reboots, so also synchronize the CMOS RTC (as on bare metal).
>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
> arch/x86/xen/time.c | 5 +++++
> 1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 0296a95..5e7f536 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -14,6 +14,7 @@
> #include <linux/kernel_stat.h>
> #include <linux/math64.h>
> #include <linux/gfp.h>
> +#include <linux/mc146818rtc.h>
>
> #include <asm/pvclock.h>
> #include <asm/xen/hypervisor.h>
> @@ -208,6 +209,10 @@ static int xen_set_wallclock(unsigned long now)
> if (!xen_initial_domain())
> return -1;
>
> + /* Set the hardware RTC. */
> + mach_set_rtc_mmss(now);

So how does this work? Is the hypervisor traping on the RTC CMOS clock?

> +
> + /* Set the Xen wallclock. */
> op.cmd = XENPF_settime;
> op.u.settime.secs = now;
> op.u.settime.nsecs = 0;
> --
> 1.7.2.5

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Re: [PATCH 1/3] xen: sync the CMOS RTC as well as the Xen wallclock [ In reply to ]

david.vrabel at citrix

Oct 12, 2012, 9:13 AM

Post #3 of 3 (146 views)

Permalink

On 12/10/12 15:57, Konrad Rzeszutek Wilk wrote:
> On Fri, Oct 12, 2012 at 01:57:12PM +0100, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@citrix.com>
>>
>> If NTP is used in dom0 and it is synchronized to its clock source,
>> then the kernel will periodically synchronize the Xen wallclock with
>> the system time. Updates to the Xen wallclock do not persist across
>> reboots, so also synchronize the CMOS RTC (as on bare metal).
>>
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>> ---
>> arch/x86/xen/time.c | 5 +++++
>> 1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
>> index 0296a95..5e7f536 100644
>> --- a/arch/x86/xen/time.c
>> +++ b/arch/x86/xen/time.c
>> @@ -14,6 +14,7 @@
>> #include <linux/kernel_stat.h>
>> #include <linux/math64.h>
>> #include <linux/gfp.h>
>> +#include <linux/mc146818rtc.h>
>>
>> #include <asm/pvclock.h>
>> #include <asm/xen/hypervisor.h>
>> @@ -208,6 +209,10 @@ static int xen_set_wallclock(unsigned long now)
>> if (!xen_initial_domain())
>> return -1;
>>
>> + /* Set the hardware RTC. */
>> + mach_set_rtc_mmss(now);
>
> So how does this work? Is the hypervisor traping on the RTC CMOS clock?

It's works the same as with the RTC driver. I think the hypervisor
allows dom0 access to the relevant I/O ports.

It's worth pointing out that mach_set_rtc_mmss() only sets the minutes
and seconds so it doesn't handle big step changes which is why
update_persistent_clock() is only called once NTP is synchronized.

David

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