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] Ticket spinlocks and MP guests

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Espen Skoglund" <espen.skoglund@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Ticket spinlocks and MP guests
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Fri, 15 Feb 2008 16:42:03 +0800
Delivery-date: Fri, 15 Feb 2008 00:44:02 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <C3DAFF98.1404E%Keir.Fraser@xxxxxxxxxxxx>
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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <D470B4E54465E3469E2ABBC5AFAC390F024D8F7B@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <C3DAFF98.1404E%Keir.Fraser@xxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AchvHZx52xVv2tsQEdyZRwAWy6hiGQAUAqPwAA+TMGsAAAamMAAAdQjMAAAAFCA=
Thread-topic: [Xen-devel] Ticket spinlocks and MP guests
>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx] 
>Sent: 2008年2月15日 16:37
>On 15/2/08 08:27, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>>> Side effect of ticket-based locks, or pv'ed sleeping locks?
>>> -- Keir
>> Side effect about pv'ed sleeping locks, since originally maybe
>> dozens of cycles are used to spin lock while pv'ed locks force
>> hypercall to Xen and may even require owner with another
>> unlock hypercall to notify back?
>You would of course spin for a while and only then sleep. 
>That's a standard
>mutex implementation trick.

I'm not sure how to define 'a while', since even for same critical
section the spin cycles varies at different point. You always risk
adding more overhead than a normal spin loop. But well, it depends
on how frequent forementioned case may occur, and the gain
of pv'ed spinlock may be larger than overhead it causes. 


Xen-devel mailing list