TSC Timecounter and multi-core/SMP

[Julian Elischer]

Daniel O'Connor wrote:
> On Fri, 18 Apr 2008, Julian Elischer wrote:
>> David O'Brien wrote:
>>> The TSC on K8 is not invariant - its rate of change is affected by
>>> P-state changes.
>>>
>>> The TSC on Greyhound (Family 10h) is invariant.
>>> [but as stated above, is not synced with other cores]
>> You'd think that an invariant sync'd clock (fast to read) of some
>> type would have been done by someone by now.. The software people
>> have been asking for this for the last decade at least.
> 
> Probably because it's very very difficult to get right :)	

and they've had over 20 years to think of something.

>