Bug 641915 - backward time drift in RHEL4, 5, and 6 Xen HVM guests that use PM timer / bug in hypervisor routine pmt_update_time() [rhel-5.5.z]
Summary: backward time drift in RHEL4, 5, and 6 Xen HVM guests that use PM timer / bug...
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: kernel-xen
Version: 5.5
Hardware: x86_64
OS: Linux
high
high
Target Milestone: rc
: ---
Assignee: Jiri Pirko
QA Contact: Red Hat Kernel QE team
URL:
Whiteboard:
Depends On: 633028
Blocks:
TreeView+ depends on / blocked
 
Reported: 2010-10-11 14:08 UTC by RHEL Program Management
Modified: 2015-05-05 01:21 UTC (History)
11 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
A Red Hat Enterprise Linux 4, 5, and 6 Xen HVM guest that uses PM timer for time keeping had the time drift backwards about 5 seconds per minute. This was caused by small inaccuracies in truncating in the pmt_update_time() function. With this update, time is kept accurately and no longer drifts backwards.
Clone Of:
Environment:
Last Closed: 2010-11-09 18:09:29 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2010:0839 0 normal SHIPPED_LIVE Moderate: kernel security and bug fix update 2010-11-09 18:06:20 UTC

Description RHEL Program Management 2010-10-11 14:08:48 UTC 
This bug has been copied from bug #633028 and has been proposed
to be backported to 5.5 z-stream (EUS).
Comment 2 Jiri Pirko 2010-10-16 09:05:30 UTC 
in kernel 2.6.18-194.21.1.el5

xen-hvm-correct-accuracy-of-pmtimer.patch
Comment 4 Jinxin Zheng 2010-10-29 06:32:39 UTC 
I've tested the reproducer in the tracked bug. Issue reproduced on all the 3 guests - RHEL4, RHEL5, RHEL6 HVM with the specific kernels.

I performed the test on kernel-xen-2.6.18-194.15.1.el5, selecting the PM timer in the guest, then running the constantly gettimeofday() code.

At the beginning, I confirmed that the time difference between host and guest is no more than 2 seconds, simply using the date command. After running the program about 10 minutes, the difference has increased to about 50 to 60 seconds.

Then I updated the kernel-xen package to kernel-xen-2.6.18-194.24.1.el5 from the errata link, rebooted the host and performed the test again. This time the time difference between host and guest has no noticeable change after running the program in the guest for more than 20 minutes.

I also did this test on the 3 different guests simultaneously. Again the time drift issue does not occur on the new hypervisor, no matter how long the program runs.

As a result I believe this bug could be put into VERIFIED.
Comment 6 errata-xmlrpc 2010-11-09 18:09:29 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2010-0839.html
Comment 8 Martin Prpič 2010-11-11 14:05:34 UTC 
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
A Red Hat Enterprise Linux 4, 5, and 6 Xen HVM guest that uses PM timer for time keeping had the time drift backwards about 5 seconds per minute. This was caused by small inaccuracies in truncating in the pmt_update_time() function. With this update, time is kept accurately and no longer drifts backwards.
Note You need to log in before you can comment on or make changes to this bug.