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[Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options and d

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options and disable unsupported config options.
From: Zachary Amsden <zach@xxxxxxxxxx>
Date: Thu, 15 Feb 2007 22:15:27 -0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, Andi Kleen <ak@xxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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Jeremy Fitzhardinge wrote:
The XEN config option enables the Xen paravirt_ops interface, which is
installed when the kernel finds itself running under Xen. (By some
as-yet fully defined mechanism, implemented in a future patch.)

Xen is no longer a sub-architecture, so the X86_XEN subarch config
option has gone.

The disabled config options are:
- PREEMPT: Xen doesn't support it
- HZ: set to 100Hz for now, to cut down on VCPU context switch rate.
  This will be adapted to use tickless later.
- kexec: not yet supported

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Signed-off-by: Ian Pratt <ian.pratt@xxxxxxxxxxxxx>
Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>

We do support different HZ values, although 100HZ is actually preferable for us, so I don't object to that. PREEMPT is supported by us, but not as tested as I would like, so I also don't object to dropping it for generic paravirt guests - Rusty - Avi any objections to dropping preempt in terms of lguest/KVM paravirtualization?

Paravirt-ops definitely needs a hook for kexec, although we should not disable kexec for the natively booted paravirt-ops. Eric - is there a way to disable it at runtime?

We do support the doublefault task gate, and it would be good to keep it, but I can't complain so much if it is gone from generic paravirt kernels for now, because it is non-essential, and generally fatal anyway. We do need it for native boots of paravirt-ops kernels, however, so turning off the config option still needs to be revisited.

Zach

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