Re: Intel P6 vs P7 system call performance

[H. Peter Anvin]

Pavel Machek wrote:
> Hi!
> 
> 
>>>>don't many of the multi-CPU problems with tsc go away because you've got a
>>>>per-cpu physical page for the vsyscall?
>>>>
>>>>i.e. per-cpu tsc epoch and scaling can be set on that page.
>>>
>>>Problem is that cpu's can randomly drift +/- 100 clocks or so... Not
>>>nice at all.
>>>
>>
>>ญญ?100 clocks is what... ?50 ns these days?  You can't get that kind of
>>accuracy for anything outside the CPU core anyway...
> 
> 50ns is bad enough when it makes your time go backwards.
> 

Backwards??  Clock spreading should make the rate change, but it should
never decrement.

	-hpa