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Re: [Xen-devel] vsyscall support in 2.6.{32,33}

To: Pasi Kärkkäinen <pasik@xxxxxx>
Subject: Re: [Xen-devel] vsyscall support in 2.6.{32,33}
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 21 Sep 2010 10:31:55 -0700
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>, Drew Jones <drjones@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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 On 09/21/2010 06:09 AM, Pasi Kärkkäinen wrote:
> On Tue, Sep 21, 2010 at 02:49:17PM +0200, Paolo Bonzini wrote:
>> Besides the obvious fact that the required hypercall is not supported by  
>> any released hypervisor, is there any other reason why the xen vsyscall  
>> code is not in the pvops/stable-2.6.{32,33}.x branches?
>> Thanks!
> I guess Jeremy didn't remember to merge it yet? :)
> Or is there some problem with it?

The main problem is that I'm not sure that the Xen clock algorithm can
give strict enough monotonicity for usermode use (ie, can't meet the
expected behaviour of clock_gettime()), and its not at all clear how to
fix it.  I could prevent non-monotonicity within one process, but not
between processes.


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