linux-kernel - Re: [patch 14/21] Xen-paravirt: Add XEN config options and disable unsupported config options.

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Message-ID: <45D54BFF.80100@vmware.com>
Date:	Thu, 15 Feb 2007 22:15:27 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Andi Kleen <ak@....de>, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, Chris Wright <chrisw@...s-sol.org>,
	Ian Pratt <ian.pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>,
	Avi Kivity <avi@...ranet.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [patch 14/21] Xen-paravirt: Add XEN config options and disable
 unsupported config options.

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@...source.com>
> Signed-off-by: Ian Pratt <ian.pratt@...source.com>
> Signed-off-by: Christian Limpach <Christian.Limpach@...cam.ac.uk>
> Signed-off-by: Chris Wright <chrisw@...s-sol.org>
>   

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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