Kernel clock issue "Clocksource tsc unstable"

[Ray Parrish]

Rashkae wrote:
>> One message I did grab says:
>>
>>  06:05:11 dio kernel: [1617517.563814] Clocksource tsc unstable (delta = 4686705598 ns)
>>  06:05:11 dio kernel: [1617517.573798] Time: acpi_pm clocksource has been installed.
>>
>> That was during a time server sync. In exactly 6 hours (at 12:05) that
>> same day, the clock stopped updating, logging stopped, ssh was fubar,
>> and I had to physically go to the datacenter and hit the reset button
>> to fix it.
>>     
>> Sorry I can't really give you a canonical answer.  tsc is an infamously
>> poor time keeper, but the kernel devs seem to prefer it over hpet
>> (Intel's High Precision Event Timer) because of performance.  (tsc is
>> right in the cpu, wheras hpet needs to access a chip on the mobo).
>>
>> On my hard system where hpet is available, hardy defaults to that.
>> However, some systems do not have hpet, and kernel defaults to tsc.  In
>> your case, tsc is deemed unstable and switches to acpi.  Why this would
>> cause your clock to stop updating however, is a mystery, unless the acpi
>> hardware on your system is broken.
>>
>> The first step to resoling this, however, will be to determine what
>> clocksources you have available, and then choose one on boot (as a
>> kernel boot parameter.)
>>
>> sudo cat /sys/devices/system/clocksource/clocksource0/available_clocksource
>>
>> and:
>>
>>  sudo cat /sys/devices/system/clocksource/clocksource0/current_clocksource
>>
>> You can specify one of the available clocksources by editing your grub
>> menu.lst file and appending a clocksource= option to the kernel you
>> boot.  For example, you can try clocksource=acpi_pm and test if acpi
>> works if you boot with it rather than switch to it.  If acpi_pm doesn't
>> work reliably on your systems, I would then try hpet or pit if those are
>> available.
>>
>>
>>     
Hello,

Sorry to butt in here, but I also receive the error messages about 
clocksource tsc being unstable. I ran the command for available 
clocksources and got the following output. "acpi_pm pit jiffies tsc" My 
system switches to acpi_pm after the error message, but I would like to 
read about the other available clocksource files before making a 
decision on which to try to use from the menu.lst file.

The problem is that I cannot find any documentation on them on my 
system. I used grep to search both the /usr/share/man and /usr/share/doc 
folders for "clocksource" and came up empty. The same search on just 
"clock" only comes up with desktop clocks and the hwclock man pages.

Do you know where I can read about the alternative clocksource files?

Thanks, Ray Parrish

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