| |
|
 |
|
 |
|
|
|
| |
|
|
xen-devel
Re: [Xen-devel] [PATCH 05/12] xen/pvclock: add monotonicity check
|
To: |
Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> |
|
Subject: |
Re: [Xen-devel] [PATCH 05/12] xen/pvclock: add monotonicity check |
|
From: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
|
Date: |
Thu, 15 Oct 2009 12:19:22 -0700 |
|
Cc: |
Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, kurt.hackel@xxxxxxxxxx, arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, chris.mason@xxxxxxxxxx |
|
Delivery-date: |
Thu, 15 Oct 2009 12:19:45 -0700 |
|
Envelope-to: |
www-data@xxxxxxxxxxxxxxxxxxx |
|
In-reply-to: |
<c7f37ead-3cf2-4277-a44e-425a7b940d31@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: |
<c7f37ead-3cf2-4277-a44e-425a7b940d31@default> |
|
Sender: |
xen-devel-bounces@xxxxxxxxxxxxxxxxxxx |
|
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20090922 Fedora/3.0-2.7.b4.fc11 Lightning/1.0pre Thunderbird/3.0b4 |
On 10/15/09 06:27, Dan Magenheimer wrote:
> I understand but you are now essentially emulating a
> reliable platform timer with a potentially unreliable
> (but still high resolution) per-CPU timer AND probably
> delivering that result to userland.
>
> Read_tsc should only be used if either CONSTANT_TSC
> or TSC_RELIABLE is true, so read_tsc is guaranteed
> to be monotonically-strictly-increasing by hardware
> (and enforced for CONSTANT_TSC by check_tsc_warp
> at boot).
>
read_tsc clearly isn't expected to produce absolutely globally monotonic
results; if it were then the check wouldn't be necessary.
J
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
|
|
| |
|
Home