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

RE: [Xen-devel] rdtscP and xen (and maybe the app-tsc answer I've been l

To: "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>
Subject: RE: [Xen-devel] rdtscP and xen (and maybe the app-tsc answer I've been looking for)
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Mon, 21 Sep 2009 15:18:41 +0100
Cc: kurt.hackel@xxxxxxxxxx, JeremyFitzhardinge <jeremy@xxxxxxxx>, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "<Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
Delivery-date: Mon, 21 Sep 2009 07:19:10 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <452c122d-4867-4ce7-9c3a-0e0396833a8a@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>
References: <4AB752B20200007800015E66@xxxxxxxxxxxxxxxxxx> <452c122d-4867-4ce7-9c3a-0e0396833a8a@default>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>>> Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> 21.09.09 16:04 >>>
>> >>> Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> 18.09.09 22:27 >>>
>> >Guest app must have some capability of getting 64-bit
>> >pvclock parameters directly from Xen without OS changes,
>> >e.g. emulated userland wrmsr, userland hypercall,
>> >or userland mapped shared page.  (This will be done
>> >rarely so need not be fast! But it does create
>> >a new userland<->Xen ABI that must be kept compatible.)
>> 
>> Are you sure this will indeed be infrequent enough? On my supposedly
>> constant-TSC AMD box, I see Xen quite frequently apply small error
>> correction factors to keep TSC from running ahead of HPET/PMTIMER.
>
>I'd like to hear from Keir on this, but I'd
>guess that this would be either a bug or a
>remnant of or inaccuracy in an old algorithm.
>
>Also if you could provide more information, I'd
>like to see if I can reproduce it on my Intel
>constant_tsc machines.
 
Not sure what further detail you mean - all that it is you would want to
look for are cases where error_factor is non-zero in
local_time_calibration() (or local time getting warped forward in the
same function; but I can only say for sure that the former does happen
not infrequently in terms of the percentage of executions of
local_time_calibration() - of course, that function itself doesn't run
very frequently).

Jan


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

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