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[Xen-devel] Re: [PATCH] xen: drop anti-dependency on X86_VISWS

To: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] xen: drop anti-dependency on X86_VISWS
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 08 Apr 2011 08:25:50 -0700
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On 04/07/2011 11:38 PM, Ian Campbell wrote:
>> Not really.  The TSC register is a requirement, but that's going to be
>> present on any CPU which can boot Xen.  We don't need any of the
>> kernel's TSC machinery though.
> So why the Kconfig dependency then? In principal a kernel compiled for a
> non-TSC processor (which meets the other requirements for Xen, such as
> PAE support) will run just fine under Xen on a newer piece of hardware.

Not sure where it came from.  It was probably never needed, or just
added for some secondary effect we wanted.

> Is there any downside to this patch (is X86_CMPXCHG in the same sort of
> boat?)

Only if we don't use cmpxchg in shared memory with other domains or the
hypervisor.  (I don't think it will dynamically switch between real and
emulated cmpxchg depending on availability.)


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