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

To: Carsten Schiers <carsten@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: AW: RE: [Xen-devel] Huge Time went backwards
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 6 Apr 2009 20:59:51 +0000 (GMT)
Cc: "Tim.Deegan" <Tim.Deegan@xxxxxxxxxx>
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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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