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[Xen-devel] Xen 4 TSC problems

To: xen-devel@xxxxxxxxxxxxxxxxxxx, Xen Users <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Xen 4 TSC problems
From: Olivier Hanesse <olivier.hanesse@xxxxxxxxx>
Date: Wed, 23 Feb 2011 11:49:49 +0100
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I've got an issue about time keeping with Xen 4.0 (Debian squeeze release). 

My problem is here (hopefully I amn't the only one, so there might be a bug somewhere) : http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=599161#50
After some times,  I got this error : Clocksource tsc unstable (delta = -2999660334211 ns). It has happened on several servers. 

Looking at the output of "xm debug-key s;"

(XEN) TSC has constant rate, deep Cstates possible, so not reliable, warp=2850 (count=3)

I am using a "Intel(R) Xeon(R) CPU L5420  @ 2.50GHz", which has the "constant_tsc", but not the "nonstop_tsc" one.
On other systems with a newer cpu with "nonstop_tsc", I don't have this issue (systems are running the same distros with same config).

I tried to boot with "max_cstate=0", but nothing changed, my TSC isn't reliable and after some times, I will got the "50min" issue again.

I don't understand how a system can do a jump of "50min" in the future. Why 50min ? it is not 40min, not 1 hour, it is always 50min.
I don't know how to make my TSC "reliable" (I already disable everything about Powerstate in BIOS Settings).

Any ideas ?


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