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): kernel-rt-2.6.24.7-101 kernel-rt-2.6.24.7-108 kernel-rt-2.6.24.7-111 How reproducible: always Steps to Reproduce: Boot into any one of 2.6.24.7-101, 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 2.6.24.7-93 (and earlier) do not exhibit this behaviour.
Andrew -- Can you attach a fresh dmesg from this host, and the output of: head /sys/devices/system/clocksource/clocksource0/* --chris
Created attachment 347384 [details] dmesg output from 2.6.24.7-117
# 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 <== hpet
Andrew, Issue is resolved in 2.6.24.7-119 and will be going into MRG 1.2. Paul
Verified in mrg-rt.git as commit 2ff40aa32a4fbdff147ed64f4bac8f1b5425adf1 and found in kernel-rt-2.6.24.7-126 SRPM.
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-2009-1157.html