 Dear Josh, I think I have found the solution to this problem, thanks to the post here: [URL] This server was booting a kernel (2.6.32-358.18.1.el6.x86_64) with the options "acpi=off noapic". The solution was to remove those options. After rebooting the server I have noticed two changes. First, the output of the available clocksources: cat /sys/devices/system/clocksource/clocksource0/available_clocksource was:  tsc jiffies and now is: tsc hpet acpi_pm On the other hand, the output for "dmesg | grep -i clock" was:  Clocksource tsc unstable (delta = 568832927 ns).  Enable clocksource failover by adding clocksource_failover kernel parameter. and that message was displayed twice per second approximately. Now is: hpet clockevent registeredSwitching to clocksource hpetrtc_cmos 00:04: setting system clock to 2013-09-20 08:46:50 UTC (1379666810)Refined TSC clocksource calibration: 2260.999 MHz.Switching to clocksource tsc which seems to be the correct output. I hope this is useful for others too! Best regards, Sebastian. 
 Dear All, I am running RHEL 6.4 in a PowerEdge R910.  When I do: # dmesg | grep -i clock I am getting a lot of messages with this text: "Clocksource tsc unstable (delta = 580433372 ns).  Enable clocksource failover by adding clocksource_failover kernel parameter." I have been looking for a solution. Concretely, Red Hat propose the following: [URL] That is, changing the clocksource. However it did not solve the problem. Actually, when I do: cat /sys/devices/system/clocksource/clocksource0/available_clocksource my options are: tsc jiffies so when I change the clocksource to jiffies, the problem remains. I must say that the kernel writes those messages when the server is powered on/rebooted. Then, after a few minutes it stops. Have any of you had this problem? Did you find any solution? Is it a symptom for a hardware problem? Many thanks in advance for your help. Best regards, Sebastian. 
PowerEdge R910 - RHEL 6.4 - Clocksource problem