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xen-ia64-devel

RE: [Xen-ia64-devel] SMP guest and itc

To: "Alex Williamson" <alex.williamson@xxxxxx>, "Tristan Gingold" <Tristan.Gingold@xxxxxxxx>
Subject: RE: [Xen-ia64-devel] SMP guest and itc
From: "Dong, Eddie" <eddie.dong@xxxxxxxxx>
Date: Fri, 10 Feb 2006 13:04:14 +0800
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Thread-topic: [Xen-ia64-devel] SMP guest and itc
Tristan:
        This is a known issue and I ever disucssed time virtualization
with Dan for a while. 
        I prefer #1. That let domU see its ITC start from 0 at boot
time? And further more, we need to support Windows eventually.
        In the meantime, I think both #1 and #3 should co-exist. Yes,
isn't the host ITC pre-synchronized in Xen?
Eddie.

Alex Williamson wrote:
> On Thu, 2006-02-09 at 08:32 +0100, Tristan Gingold wrote:
>> Hi,
>> 
>> during boot, linux kernel tries to synchronize itc of all
>> processors.  However currently itc is not virtualized:
>> (XEN) vcpu_set_itc: Setting ar.itc is currently disabled
>> 
>> What should we do ?
>> a) virtualize ITC
>> b) para-virtualize ITC (ie, modifying linux kernel)
>> c) pre-synchronize ITC
>> 
>> I really prefer c).
> 
>    I'm not sure I understand c).  Aren't the ITCs already
> pre-synchronized by xen in smp_callin()?   Thanks,
> 
>       Alex


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