WARNING - OLD ARCHIVES

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/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] Re: TSC scaling and softtsc reprise, and PROPOSAL

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: TSC scaling and softtsc reprise, and PROPOSAL
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 27 Jul 2009 20:55:10 +0100
Cc: "Dong, Eddie" <eddie.dong@xxxxxxxxx>, John Levon <levon@xxxxxxxxxxxxxxxxx>
Delivery-date: Mon, 27 Jul 2009 12:55:35 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <2dce8618-e307-4104-b5da-35435185e9bb@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: AcoO30cnZ/pc+gpXQAS24HOZQ+no3gAFN6C8
Thread-topic: TSC scaling and softtsc reprise, and PROPOSAL
User-agent: Microsoft-Entourage/12.20.0.090605
On 27/07/2009 18:25, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> I believe this affects the guest OS executing RDTSC, not
>> guest apps, and is
>> only to delay the TSC to not 'run past' pending timer ticks
>> (typically where
>> they have been delayed due to the guest being preempted).
>> 
>>  -- Keir
> 
> Could be.  The text would lead me to believe otherwise
> though.  Read the section on "Virtual TSC" in the
> above PDF. Specifically the Virtual TSC "advances even
> when the the virtual CPU is not running" and "In the
> past, this feature had sometimes been recommended to
> improve performance of APPLICATIONS that read the
> TSC frequently..." (my emphasis)

Yes, then it sounds like they virtualise it for apps too. Also there is an
option to virtualise the TSC at a specified frequency -- that would be
pretty weird if it applied only to guest-OS RDTSCs but not guest-app RDTSCs.

Interesting...

 -- Keir



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>