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SubjectRe: [PATCH 3/3] x86/xen: sync the CMOS RTC as well as the Xen wallclock
On 05/14/2013 11:00 AM, David Vrabel wrote:
> On 14/05/13 18:24, John Stultz wrote:
>> On 05/13/2013 10:56 AM, 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 | 11 ++++++++++-
>>> 1 files changed, 10 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
>>> index a1947ac..4656165 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>
>>> @@ -199,17 +200,25 @@ static void xen_get_wallclock(struct timespec *now)
>>> static int xen_set_wallclock(const struct timespec *now)
>>> {
>>> struct xen_platform_op op;
>>> + int ret;
>>>
>>> /* do nothing for domU */
>>> if (!xen_initial_domain())
>>> return -1;
>>>
>>> + /* Set the Xen wallclock. */
>>> 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);
>>> + ret = HYPERVISOR_dom0_op(&op);
>>> + if (ret)
>>> + return ret;
>>> +
>>> + /* Set the hardware RTC. */
>>> + return mach_set_rtc_mmss(now);
>> Sorry, just noticed one more thing while applying this. Do all Xen
>> systems run on hardware that has the conventional CMOS clock?
>>
>> What happens if the bare-metal needs to use efi_set_rtc() or
>> vrtc_set_mmss() ?
> Ug. I hadn't considered that. I'll have think some more on this.

Ok. I'll look forward to a future revision then and not queue this one.


Just FYI, here's what I rewrote the commit message to:

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_set_walltime() just notifies
other domN guests that it has been updated, and does not modify
the underlying CMOS clock.

Thus, this patch modifies xen_set_wallclock() so it will set
the underlying CMOS clock when called from dom0, ensuring the
persistent_clock will be correct on the next hardware boot.


I feel its a bit more clear, but feel free to tweak it as you see fit.

thanks
-john



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