linux-kernel - Re: [Xen-devel] [PATCH 2/2] x86/xen: sync the wallclock when the system time changes

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Date:	Wed, 29 May 2013 08:42:56 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.com>,
	"John Stultz" <john.stultz@...aro.org>
Cc:	<xen-devel@...ts.xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/2] x86/xen: sync the wallclock when
 the system time changes

>>> On 28.05.13 at 20:53, John Stultz <john.stultz@...aro.org> wrote:
> On 05/28/2013 11:22 AM, David Vrabel wrote:
>>   	op.cmd = XENPF_settime;
>> -	op.u.settime.secs = now->tv_sec;
>> -	op.u.settime.nsecs = now->tv_nsec;
>> +	op.u.settime.secs = now.tv_sec;
>> +	op.u.settime.nsecs = now.tv_nsec;
>>   	op.u.settime.system_time = xen_clocksource_read();
>>   
>>   	ret = HYPERVISOR_dom0_op(&op);
>>   	if (ret)
>> -		return ret;
>> +		return 0;
>>   
>> -	/* Set the hardware RTC. */
>> -	return mach_set_rtc_mmss(now);
>> +	last = now;
>> +	next = timespec_add(now, ns_to_timespec(NSEC_PER_SEC / 2));
>>   
> 
> Am I missing the xen_set_wallclock hook here? Your previous patch wanted 
> to call the dom0 op and then set the hardware RTC.

That ought to be intentional: We should update the hypervisor's
software wall clock here, but limit updating of the RTC to whenever
a native kernel would do this (i.e. among other things subject to
CONFIG_RTC_SYSTOHC).

Jan

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