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: pvclock (PV and HVM) and vsyscall

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: [Xen-devel] Re: pvclock (PV and HVM) and vsyscall
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 15 Oct 2010 17:28:25 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Tim Deegan <Tim.Deegan@xxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Delivery-date: Fri, 15 Oct 2010 17:29:17 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <bea7d3ae-08a5-4298-8478-0af724010566@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: <bea7d3ae-08a5-4298-8478-0af724010566@default>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.4
 On 10/15/2010 08:48 AM, Dan Magenheimer wrote:
> The other discussion of RADclock reminded me:
>
> IIRC the pvclock algorithm is still incompatible with
> vsyscall/vdso (fast system calls) and there was no obvious
> and upstreamable solution to resolve this.
>
> This means that any userland call to the various gettimeofday
> routines will always do a true system call on both (a) a PV
> domain or (b) any PV on HVM domain with Stefanos' pvclock patch.
>
> Since true syscalls are very expensive on a 64-bit
> PV domain, I'm wondering if pvclock is still the right
> default choice for upstream (at least for 64-bit).

What other options are there?  If the tsc is globally stable, then using
pvclock in userspace will work fine; if it isn't, you'll need to do the
syscall anyway.

There's no basic problem with the vsyscall pvclock patch so long as we
can know under what circumstances it is safe to enable.

    J


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

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