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[Xen-users] Time sync error in Xen DomU

Hello, everybody:
   In my institute, there are hundreds of computers running Xen virtual machines. Every virtual machine runs ntpdate to sync time with the ntp servers once an hour independently(echo 1 > /proc/sys/xen/independent_wallclock in DomU and Dom0). I found that there is one virtual machine will have time sync error in one week or two weeks. Everytime the misbehavior VM is different (the physical machine is different too), however, the time sync error is the same: the VM's time go ahead 36 minutes, and then its timer stops until 36 minutes later. This time sync error makes the applications fails everytime.
   There dmesg log in D0 and xm dmesg do not have anything unnormal, and the dmesg log in the misbehavior VM is list below:
May  5 17:56:49  kernel: Badness in tcp_verify_wq at net/ipv4/tcp_ipv4.c:221
May  5 17:56:49  kernel:  [<c044c34d>] tcp_verify_wq+0x239/0x27b
May  5 17:56:49  kernel:  [<c0441db3>] tcp_ack+0x65/0x187f
May  5 17:56:49  kernel:  [<c045fff9>] ipt_do_table+0x1e7/0x322
May  5 17:56:49  kernel:  [<c0460108>] ipt_do_table+0x2f6/0x32
May  5 17:56:50  kernel:  [<c012d8c4>] autoremove_wake_function+0x0/0x3d
May  5 17:56:50  kernel:  [<c015d932>] vfs_write+0x8a/0xdd
May  5 17:56:50  kernel:  [<c015dea1>] sys_write+0x3f/0x6
May  5 17:56:50  kernel:  [<c0104c8d>] syscall_call+0x7/0xb          
Above warning dues to lack of memory, and kernel kills some processes.
May  5 17:57:01  /usr/sbin/cron[14544]:                                      
At this time, timer goes ahead 36 minutes, and then the timer stops.
When 36 minutes later, timer works again.
May  5 18:33:05  /usr/sbin/cron[14598]:                                      
May  5 18:33:05  sshd[2790]:
May  5 18:33:05  sshd[14659]:
   The version of xen is xen-3.2.0-16718-14-0.4, and the version of linux is SUSE- The CPU is Intel xeon E5405, memory is 2G, and there are 4 DomU VMs in one physical machine. Although the CPU is 64-bit, the Xen and Linux is 32-bit version.
   36 minutes are 2,160,000,000 ms, and 2160000000 = 0X 80BEFC00. In 32-bit system, does it caused by overflowing of some time-keeping variables?
   For some reasons, I could not update the version of xen or linux to the latest one.
   Could anybody help me to deal with this time sync error? Thank you very much for your help!
Xiang Zhang
National Research Center for Intelligent Computing Systems
Institute of Computing Technology
Chinese Academy of Sciences
Jun 18th, 2009
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