From: Keir Fraser <keir@xen.org>
To: Henry Pepper <henrypepr@gmail.com>, xen-devel@lists.xensource.com
Subject: Re: common time reference between domU and dom0
Date: Fri, 10 Dec 2010 10:03:39 +0000 [thread overview]
Message-ID: <C927AB7B.C5A2%keir@xen.org> (raw)
In-Reply-To: <AANLkTinHMjTXRHgkDaKMSw7hGehqPZZBpA1dJ-0W+au1@mail.gmail.com>
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@gmail.com> 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@xen.org> wrote:
>> System time, as exposed to guests by Xen, should be good enough.
>>
>> -- Keir
>>
>>
>> On 10/12/2010 05:23, "James Harper" <james.harper@bendigoit.com.au> 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@lists.xensource.com
>>> http://lists.xensource.com/xen-devel
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xensource.com
>> http://lists.xensource.com/xen-devel
>>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
prev parent reply other threads:[~2010-12-10 10:03 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-10 5:23 common time reference between domU and dom0 James Harper
2010-12-10 7:19 ` Keir Fraser
2010-12-10 8:23 ` James Harper
2010-12-10 10:00 ` Keir Fraser
2010-12-10 10:20 ` James Harper
2010-12-10 10:22 ` Paolo Bonzini
2010-12-10 10:45 ` Keir Fraser
2010-12-10 20:27 ` Dan Magenheimer
2010-12-10 21:41 ` Paolo Bonzini
2010-12-10 10:45 ` Keir Fraser
2010-12-10 10:51 ` Tim Deegan
2010-12-10 20:24 ` Dan Magenheimer
2010-12-10 8:26 ` Henry Pepper
2010-12-10 10:03 ` Keir Fraser [this message]
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