linux-kernel - Re: [Xen-devel] Re: [PATCH] x86/pvclock-xen: zero last

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Message-ID: <95805e88-b6d5-4ae2-9351-9e458656cfb8@email.android.com>
Date:	Wed, 27 Oct 2010 13:59:54 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Glauber Costa <glommer@...hat.com>
CC:	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	kvm-devel <kvm@...r.kernel.org>,
	Eelco Dolstra <e.dolstra@...elft.nl>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Olivier Hanesse <olivier.hanesse@...il.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [Xen-devel] Re: [PATCH] x86/pvclock-xen: zero last_value on resume

I'll check it this evening when I'm at a working network again :(

"Jeremy Fitzhardinge" <jeremy@...p.org> wrote:

> On 10/26/2010 10:48 AM, Glauber Costa wrote:
>> On Tue, 2010-10-26 at 09:59 -0700, Jeremy Fitzhardinge wrote:
>>> If the guest domain has been suspend/resumed or migrated, then the
>>> system clock backing the pvclock clocksource may revert to a smaller
>>> value (ie, can be non-monotonic across the migration/save-restore).
>>> Make sure we zero last_value in that case so that the domain
>>> continues to see clock updates.
>>>
>>> [ I don't know if kvm needs an analogous fix or not. ]
>> After migration, save/restore, etc, we issue an ioctl where we tell
>> the host the last clock value. That (in theory) guarantees
>monotonicity.
>>
>> I am not opposed to this patch in any way, however.
>
>Thanks.
>
>HPA, do you want to take this, or shall I send it on?
>
>Thanks,
>    J

-- 
Sent from my mobile phone.  Please pardon any lack of formatting.
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