Bug 502893 - TSC synchronisation fails on Nehalem
TSC synchronisation fails on Nehalem
Product: Red Hat Enterprise MRG
Classification: Red Hat
Component: realtime-kernel (Show other bugs)
x86_64 Linux
low Severity high
: 1.1.5
: ---
Assigned To: Red Hat Real Time Maintenance
David Sommerseth
Depends On:
  Show dependency treegraph
Reported: 2009-05-27 12:20 EDT by Andrew Gilligan
Modified: 2016-05-22 19:28 EDT (History)
6 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2009-07-14 15:11:56 EDT
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
dmesg output from (54.77 KB, text/plain)
2009-06-11 07:24 EDT, Andrew Gilligan
no flags Details

  None (edit)
Description Andrew Gilligan 2009-05-27 12:20:53 EDT
Description of problem:
Kernel messages show that TSC synchronisation fails between cores on Nehalem-based systems.

A notable side-effect of this is that gettimeofday() calls take approximately 20 times longer to return.
A simple C program calling gettimeofday() 10 million times should take 0.3 seconds - on the affected kernels this takes 5.8 seconds.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
Boot into any one of, 108 or 111 on a Nehalem machine.
Actual results:
kernel: Intel(R) Xeon(R) CPU           X5570  @ 2.93GHz stepping 05
kernel: checking TSC synchronization [CPU#0 -> CPU#1]:
kernel: Measured 4 cycles TSC warp between CPUs, turning off TSC clock.
kernel: Marking TSC unstable due to check_tsc_sync_source failed

Expected results:
kernel: Intel(R) Xeon(R) CPU           X5570  @ 2.93GHz stepping 05
kernel: checking TSC synchronization [CPU#0 -> CPU#1]: passed.

Additional info:
Kernels (and earlier) do not exhibit this behaviour.
Comment 1 Chris Van Hoof 2009-06-02 13:12:04 EDT
Andrew -- Can you attach a fresh dmesg from this host, and the output of:

head /sys/devices/system/clocksource/clocksource0/*

Comment 12 Andrew Gilligan 2009-06-11 07:24:59 EDT
Created attachment 347384 [details]
dmesg output from
Comment 13 Andrew Gilligan 2009-06-11 07:25:58 EDT
# head /sys/devices/system/clocksource/clocksource0/*
==> /sys/devices/system/clocksource/clocksource0/available_clocksource <==
hpet acpi_pm jiffies tsc 

==> /sys/devices/system/clocksource/clocksource0/current_clocksource <==
Comment 16 Paul Batkowski 2009-06-23 11:06:57 EDT

Issue is resolved in and will be going into MRG 1.2. 

Comment 19 David Sommerseth 2009-07-09 11:14:53 EDT
Verified in mrg-rt.git as commit 2ff40aa32a4fbdff147ed64f4bac8f1b5425adf1 and found in kernel-rt- SRPM.
Comment 21 errata-xmlrpc 2009-07-14 15:11:56 EDT
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.


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