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Re: [Xen-devel] common time reference between domU and dom0

To: Henry Pepper <henrypepr@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>

From: Keir Fraser <keir@xxxxxxx>

Date: Fri, 10 Dec 2010 10:03:39 +0000

Cc:

Delivery-date: Fri, 10 Dec 2010 02:05:44 -0800

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List-id: Xen developer discussion <xen-devel.lists.xensource.com>

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Thread-topic: [Xen-devel] common time reference between domU and dom0

All domains have access to Xen system time, either via hypercall or by calculating it themselves directly given information Xen provides in shared memory. Time interrupt/events can't really be missed - they are delivered synchronously to the guest. -- Keir On 10/12/2010 08:26, "Henry Pepper" <henrypepr@xxxxxxxxx> wrote: > I was under the impression that none of the domains has the correct time. > Neither Dom0 nor DomU receives a timer interrupt, but only a timer > event. Events that could be missed. > So timing in the millisecond can have jitter and drift. > Is there actually a way to keep a precise timer in a domain? > > On top of this I would think that both domains would have to have > exclusive access to their own CPU in order to avoid being switched off > of the CPU in periods of time(quantums of 30 ms using the default > scheduler). > > Henry > > On Fri, Dec 10, 2010 at 8:19 AM, Keir Fraser <keir@xxxxxxx> wrote: >> System time, as exposed to guests by Xen, should be good enough. >> >> -- Keir >> >> >> On 10/12/2010 05:23, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote: >> >>> I would like to be able to measure front/back ring message latency >>> between a Windows DomU and Dom0. To do this I need a common time >>> reference between the two, preferably with at least microsecond >>> precision (latency <1us is irrelevant for my purposes). Does such a >>> thing exist? A small amount of overhead in measuring this latency is >>> acceptable. >>> >>> Thanks >>> >>> James >>> >>> >>> _______________________________________________ >>> Xen-devel mailing list >>> Xen-devel@xxxxxxxxxxxxxxxxxxx >>> http://lists.xensource.com/xen-devel >> >> >> >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@xxxxxxxxxxxxxxxxxxx >> http://lists.xensource.com/xen-devel >> > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel

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