[ kvm-Bugs-1900228 ] Time on guest slows down sometimes...

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Bugs item #1900228, was opened at 2008-02-23 10:26
Message generated for change (Comment added) made by glommer
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Category: amd
Group: None
Status: Open
Resolution: None
Priority: 6
Private: No
Submitted By: stevie1024 (stevie1024)
Assigned to: Nobody/Anonymous (nobody)
Summary: Time on guest slows down sometimes...

Initial Comment:
I run kvm version 60 on an linux 2.6.24 kernel on an AMD 64 processor (see below for details).

I installed 2 guest machines, one linux and one windows (XP) and started them both. The clocks on both guests are sometimes slowed down.

If e.g. I play some youtube clips on the Windows guest, the clock of the Windows guest starts lagging about 15% (time is about 15% slower than host, or real, time).

If I cause some load on the linux guest, e.g. with 'tar jcvf test /usr', the clock of this guest also runs about 5% slower. And there's a message in the client syslog saying 'warning: many lost ticks, Your time source seems to be instable or some driver is hogging interupts'.

Running e.g. 'tar jcvf test /usr' on the host doesn't have any influence on the guest clocks.

I think this is quite a serious bug, as 'ntp' can't compensate for this instability. If I understand correctly ntp can only compensate for clocks that are too slow or too fast by a reasonably fixed (low) percentage.


/proc/cpuinfo:

processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 95
model name      : AMD Athlon(tm) Processor LE-1600
stepping        : 3
cpu MHz         : 2204.998
cache size      : 1024 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow up rep_good pni cx16 lahf_lm svm extapic cr8_legacy
bogomips        : 4413.24
TLB size        : 1024 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts fid vid ttp tm stc

uname -a:

Linux bigbird 2.6.24-1-amd64 #1 SMP Mon Feb 11 13:47:43 UTC 2008 x86_64 GNU/Linux

clients were started with:

kvm -m 1024 -usb -hda wxp_test.img -net nic,vlan=0 -net user,vlan=0,hostname=wxp-test  -boot c  -vnc :0

and

kvm -m 512 -usb -hda debian_server.img -net nic,vlan=0 -net user,vlan=0,hostname=debian-server -vnc :1



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Comment By: Glauber de Oliveira Costa (glommer)
Date: 2010-06-25 17:01

Message:
Specially for windows guests, the option -rt-td-hack may be helpful. For
linux guests, if you can run a new enough guest, using a guest with
kvmclock can make the clock go in sync .

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Comment By: stevie1024 (stevie1024)
Date: 2008-02-23 10:32

Message:
Logged In: YES 
user_id=2017347
Originator: YES

I forgot to mention, I think bug 1826080 is related to this, but I think
my description is more general.

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