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] [RFC] Physical hot-add cpus and TSC

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, "Xen-Devel (xen-devel@xxxxxxxxxxxxxxxxxxx)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] Physical hot-add cpus and TSC
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 28 May 2010 17:08:36 +0100
Delivery-date: Fri, 28 May 2010 09:09:45 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <23411061-56ab-4d16-b8f1-5bba0f37c165@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: Acr+czhBF6feJv2sQCmP9D2I6yluNQADM6+R
Thread-topic: [Xen-devel] [RFC] Physical hot-add cpus and TSC
User-agent: Microsoft-Entourage/
On 28/05/2010 15:35, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> "Undetectable" by Dan's definition means undetectable by
>> a multi-threaded app on a multi-vcpu guest. Any detected
>> warp would therefore be a problem.
> This is actually Linux's definition, a requirement
> for selecting tsc as Linux's default clocksource,
> and measured by the same algorithm in Xen and Linux.

Well, to be precise, it's Linux's definition for whether TSC is a suitable
basis for the kernel's monotonic clock source. Linux doesn't make strong
guarantees to applications about TSC semantics, by synthesising TSC, or
anything like that. Applying the same constraints on the TSC all the way up
to application level was your own proposal.

Anyhow, retreading this argument is not going to be fruitful. It's fair to
say that your definition is now also Xen's definition.

 -- Keir

Xen-devel mailing list