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


[Xen-devel] RE: pv_ops (2.6.31) and CONFIG_NO_HZ

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] RE: pv_ops (2.6.31) and CONFIG_NO_HZ
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 2 Nov 2009 16:06:10 -0800 (PST)
Cc: "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Mon, 02 Nov 2009 16:07:35 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4AEF6045.2060001@xxxxxxxx>
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
> On 11/02/09 13:45, Dan Magenheimer wrote:
> > Has anyone looked at using CONFIG_NO_HZ with an upstream
> > pv_ops kernel?  This seems like an intelligent combination...
> > since pvclock is a good timesource, it seems like there
> > should be no reason to have a regular tick, and one
> > could pack more idle domains into one physical machine.  
> Yes, I've always recommeded NO_HZ.  The pvops kernel disables 
> the 100Hz
> periodic timer and always uses the high-precision timers for its
> clockevents.  The core kernel still asks for periodic interrupts on
> occasion, so it isn't completely tickless, but that's not really
> something we should solve at the Xen level.

OK thanks.  I'll look into this a bit further for HVMs.

> > I tried enabling CONFIG_NO_HZ from an otherwise working .config
> > file for 2.6.31 and the new kernel (running as a PV domU) 
> panics early
> > in boot ("Kernel panic -- not syncing: Attempted to kill init!"
> > with a call trace of syscall_call->sys_exit_group->do_group_exit->
> > do_exit->panic).  So I'm wondering if I did something stupid
> > or it is known to not work.

> No, that's strange.  However, someone else reported something similar
> which turns out to be triggered by the pvclock vsyscall stuff.   I
> haven't worked out what's failing yet.  (Or why NO_HZ would depend on
> it, though it might be related to the highres timers options.)

This was a kernel.org 2.6.31 kernel, not from your git tree
so no pvclock vsyscall stuff would be in it.
(Sorry I guess the subject was confusing.)

> Can you post the full crash message?

No, most of it scrolls away in the VNC window.  But
since I now know it is supposed to work, I'll look into it


Xen-devel mailing list

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