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AW: RE: AW: RE: [Xen-devel] Huge Time went backwards

To: "dan.magenheimer" <dan.magenheimer@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: AW: RE: AW: RE: [Xen-devel] Huge Time went backwards
From: "Carsten Schiers" <carsten@xxxxxxxxxx>
Date: Mon, 6 Apr 2009 23:19:31 +0200
Cc: "Tim.Deegan" <Tim.Deegan@xxxxxxxxxx>
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Thanks Dan.

As I lost my setup (although I could have restored that - it was an 
lvm), I set
up everything new. Today I compiled Xen 3.3.1, 3.3-testing and 
3.4-unstable and
two kernel pairs for 64 and 32 bit (with and without MSI support; I have 
issues with that in one of my DomUs that gets four PCI devices passed 

As I am unsure whether I can simply install xen-unstable tools over 
3.3.1, I will
set up a copy of my Dom0 and install it there. I modified the extra 
version so 
that I can use the same boot dir and still can distinguish between the 

I still have not found anything like tagging for the kernel; the 
tar-ball for 
Xen-3.3.1 will not compile with my Xen. So for kernels, it's now the one 
today in any case.

Next step is to carefully start testing, beginning with MSI and Xen 3.4, 
as I
expect the best results there. Then I will shorten the ondemand sampling 
which is now at roughly 4 sec. This is to prevent the core to jump their 
rate too often.

In parallel, I will try to find out where exactly this message is 
produced and
what it means.

I will report ;-)

Andy yes, it's all pv, no hvm. And all DomUs get their time from 
And there seems to be no drift.

Best Regards,

-----Ursprüngliche Nachricht-----
Von: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx] 
Gesendet: Montag, 6. April 2009 23:00
An: Carsten Schiers; xen-devel
Cc: Tim.Deegan
Betreff: RE: AW: RE: [Xen-devel] Huge Time went backwards

Hi Carsten --

I think domain0 (and all PV domains) only use the
one paravirtualized clock based on xen system time.
Changing clock options such as hpet and notsc will
not affect a PV domain, only an HVM domain.


> -----Original Message-----
> From: Carsten Schiers [mailto:carsten@xxxxxxxxxx]
> Sent: Friday, April 03, 2009 11:11 AM
> To: Dan Magenheimer; xen-devel
> Cc: Tim.Deegan
> Subject: AW: RE: [Xen-devel] Huge Time went backwards
> > Interesting.  This is reported booting dom0, correct?  Are
> > you running NTP in dom0?
> It's in Dom0 log when powernow-k8 is loaded, which is after 
> loading loop 
> and prior on 
> mounting disks. Roughly 4 seconds prior to starting ntpd, so 
> I guess it 
> has no interaction.
> It feels a bit like that 3.3.1 and 3.4 set values differently 
> in the CPU 
> cores, because
> when rebooting the same Xen version two or three times again, 
> it's away. 
> It will come back
> with either Xen version when you switch version. At least it 
> feels that 
> way.
> >> If I get on your nerves with my time keeping issues
> >
> >No, it is good to raise awareness of these issues until they
> >are all fixed.  ESPECIALLY if you see time problems in xen-unstable,
> >it would be good to get them fixed before 3.4 is final.
> Unfortunately, I broke my unstable. Also, it's a 
> semi-productive family 
> server, so slots to
> Test are a bit rare. I try my best to set it up again and do more 
> testing.
> I have this Time went backwards issues from the beginning. 
> Now I tried 
> to set HPET to 32bit,
> although I don't know whether a) BIOS is read to use 32bit instead of 
> 64bit, or b) this makes
> any difference, or c) HEPT and TSC have something in common when it 
> comes to TSC drifts related
> to power management.
> I also wondered, whether I should try booting with notsc, but it's a 
> dual core and I think then
> I need TSC, or don't I?
> BR,
> Carsten.
> -----Original Message-----
> From: Carsten Schiers [mailto:carsten@xxxxxxxxxx]
> Sent: Friday, April 03, 2009 6:52 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] Huge Time went backwards
> Just an observation, to whom it may concern: when booting 
> between 3.3.1 
> and
> current xen-3.4-unstable, right after loading powernow-k8, 
> there will be 
> one huge
> Time went backwards messages (500ms upt to 1,5s), which disappears 
> unless
> you change Xen version again.
> BTW: If I get on your nerves with my time keeping issues, just drop a 
> note and 
> I keep calm ;-).
> BR,
> Carsten.

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