Kernel clock issue "Clocksource tsc unstable"

[Rashkae]

NoOp wrote:
> On 02/27/2009 06:55 PM, Rashkae wrote:
>> NoOp wrote:
>>
>>> I recall that thread:
>>> http://comments.gmane.org/gmane.linux.ubuntu.user/145397
>>> [Computer loosing time]
>>> might be worth looking at again.
>>>
>>>
>> Not really,, That thread led me to believe the problem was with my power
>> supply, which I replaced, and declared success.  However, my success was
>> very short lived.  It was afterwards that I discovered I can fix it by
>> changing my clocksource from tsc to acpm, but this was something so
>> obscure, (and it seemed, not bothering anyone else) that I never
>> bothered posting about it.
>>
> 
> But shouldn't it switch automatically to acpi_pm if tsc is not stable?[1]
> 
> For instance, on the Thinkpad A21M that I receive the dmesg of:
> Clocksource tsc unstable (delta = -87685142 ns)

yes, it should.  but stable doesn't really have much to do with
accurate... TSC is not accurate, it's not even meant to be.  (I'm not
sure exactly what kinds of problems make it unstable.  I used to think
it was synchronization between cpu cores, but apparently, there is more
to it than that.)

On systems where it works, however, TSC is very performance friendly.  I
guess the reasoning is, having an 8 core super server with dozens of
vm's is all fine and good, unless all your processes get stuck
contending for the one timer chip on your mobo.