From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH] xen: drop anti-dependency on X86_VISWS
Date: Fri, 08 Apr 2011 08:25:50 -0700
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To: Ian Campbell <Ian.Campbell@eu.citrix.com>
Cc: "randy.dunlap@oracle.com" <randy.dunlap@oracle.com>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@citrix.com>, "eric.dumazet@gmail.com" <eric.dumazet@gmail.com>, "konrad.wilk@oracle.com" <konrad.wilk@oracle.com>, David Miller <davem@davemloft.net>, "mirq-linux@rere.qmqm.pl" <mirq-linux@rere.qmqm.pl>, "mingo@redhat.com" <mingo@redhat.com>, "hpa@zytor.com" <hpa@zytor.com>, "tglx@linutronix.de" <tglx@linutronix.de>, "virtualization@lists.linux-foundation.org" <virtualization@lists.linux-foundation.org>, "pazke@donpac.ru" <pazke@donpac.ru>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

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.)

    J