This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] write_tsc in a PV domain?

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] write_tsc in a PV domain?
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 26 Aug 2009 16:58:51 +0100
Cc: "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Wed, 26 Aug 2009 08:59:37 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <6eb624ce-7d03-425b-afa4-2d97325b096c@default>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcomY8+fH7aK68+IT8uVqitZT/fFwQAAksVY
Thread-topic: [Xen-devel] write_tsc in a PV domain?
User-agent: Microsoft-Entourage/
On 26/08/2009 16:42, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> OK, I see, wrmsr_hypervisor_regs(0x10) and mce_wrmsr(0x10) and
> rdmsr_safe(0x10) all return 0, so the code at "invalid:" is
> executed and a warning is printk'd.  So in the current
> implementation, write_tsc is skipped over.
> But ARCHITECTURALLY does Xen consider write_tsc to be a no-op
> for PV domains, or is this just a case that's never been
> encountered before?  In other words, if a future PV OS had a
> good reason to write_tsc, would we implement it (and make
> the necessary adjustments to Xen's usages of tsc) or just say,
> sorry, not allowed?

There'd have to be a good argument for supporting it. I don't think we ever

 -- Keir

Xen-devel mailing list