Messages in this thread | | | Date | Tue, 14 May 2013 11:03:53 -0700 | From | John Stultz <> | Subject | Re: [PATCH 3/3] x86/xen: sync the CMOS RTC as well as the Xen wallclock |
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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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